Sejarah Teori Pengaturan / Kendali

 Sumber : Control Theory Timeline
Please note the following:
The five areas of control theory discussed below are inspired from the latest materials and survey papers available and do not by any means try to cover the multi-disciplinary and broad area of control systems.
The materials outlined below are extracted from the standard resources and the references therein. Related and appropriate references are cited but they are far from being complete.
Control Theory: A Quick Overview
Adaptive Control
Filtering and Stochastic Control
H-Infinity Control
Linear Matrix Inequality
Nonlinear Control
References
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Control Theory: A Quick Overview
1642-1754
The work of I. Newton (1642-1727) and G.W. Leibniz (1646-1716), the brothers Bernoulli (late 1600’s and early 1700’s), J. F. Riccati (1676-1754) led to the discovery of the infinitesimal calculus which in turn helped the development of differential equations theory. ([26])


1736-1865
J. L. Lagrange (1736-1813) and W. R. Hamilton (1805-1865) established the use of differential equations in analyzing the motion of dynamical systems. ([26])


1868
J. C. Maxwell analyzed the stability of Watt’s flyball governor. ([26])


1877
E. J. Routh provided a numerical technique for determining when a characteristic equation has stable roots. ([193])
I. I. Vishnegradsky analyzed the stability of regulators using differential equations independently of Maxwell. ([194])


1892
A. M. Lyapunov studied the stability of nonlinear differential equations using a generalized notion of energy. ([1], [26])


1892-1898
O. Heaviside invented operational calculus and studied the transient behavior of systems, introducing a notion equivalent to that of the transfer function. ([26])


1893
A. B. Stodola studied the regulation of a water turbine using the techniques of Vishnegradsky. ([26])


1895
A. Hurwitz solved independently the problem of determining the stability of the characteristic equation. ([195])


1920-1939
P. S. de Laplace (1749—1827), J. Fourier (1768—1830), A.L. Cauchy (1789—1857) developed the frequency domain approaches at Bell Telephone Laboratories, and explored and used these in communication systems. ([26])


1922
N. Minorsky introduced his three-term controller for the steering of ships, thereby becoming the first to use the PID controller. He considered nonlinear effects in the closed-loop system. ([199])


1927
H. S. Black demonstrated the usefulness of negative feedback. ([196])


1932
H. Nyquist developed Regeneration Theory for the design of stable amplifiers and derived his Nyquist Stability Criterion based on the polar plot of a complex function. ([197])


1938
H.W. Bode used the magnitude and phase frequency response plot of a complex function and investigated closed-loop stability using the notions of phase and gain margin. ([198])


1941
A. C. Hall recognized the deleterious effects of ignoring noise in control system design. ([200])
A. N. Kolmogorov provided a theory for discrete time stationary stochastic processes. ([203])


1942
N. Wiener analyzed information processing systems using models of stochastic processes and developed a statistically optimal filter for stationary continuous-time signals that improved the signal-to-noise ratio in a communication system while working in the frequency domain. ([159])


1945-1955
The first textbooks on Control Theory appeared which discussed straightforward design tools and provided great insight and guaranteed solutions to design problems. ([204], [205], [206], [207], [208])


1947
N. B. Nichols developed his Nichols chart for the design of feedback systems. ([26], [201])


1948
W. R. Evans presented his root locus technique, which provided a direct way to determine the closed-loop pole locations in the s-plane. ([202])


1950’s
C. E. Shannon, at Bell Labs, revealed the importance of sampled data techniques in the processing of signals. ([191])


1952
J. R. Ragazzini, G. Franklin, and L. A. Zadeh developed the theory of sampled data systems. ([214], [215])


1955
Tsypkin used the phase plane for nonlinear controls design. ([7], [8])


1957
R. Bellman applied dynamic programming to the optimal control of discrete-time systems, demonstrating that the natural direction for solving optimal control problems is backwards in time. His procedure resulted in closed-loop, generally nonlinear, feedback schemes. ([209])


1958
L. S. Pontryagin had developed his maximum principle, which solved optimal control problems relying on the calculus of variations developed by L. Euler (1707-1783). He solved the minimum-time problem, deriving an on/off relay control law as the optimal control. ([210])


1960
R. E. Kalman and J. E. Bertram publicized the vital work of Lyapunov in the time domain control of nonlinear systems. ([211])
R. E. Kalman discussed the optimal control of systems, providing the design equations for the Linear Quadratic Regulator (LQR). ([88])
R. E. Kalman developed optimal filtering and estimation theory, providing the design equations for the discrete Kalman Filter. ([81])
E. I. Jury advanced the theory of sampled data systems. ([216])


1961
R. E. Kalman and R. S. Bucy developed the continuous Kalman Filter. ([82])


1963
B. C. Kuo provided analysis and synthesis of sampled-data control systems. ([217])


1964
J. Kudrewicz formalized the use of frequency-domain techniques to systems with simple types of nonlinearities using the describing function approach which relies on the Nyquist criterion. ([26])


1964-1966
G. Zames ([11] [12]), I. W. Sandberg ([13]) , K. S. Narendra ([212]) , C. A. Desoer ([213]) , and others extended the work of Popov and Lyapunov in nonlinear stability.


1966
G. Zames presented the small gain theorem. ([11], [12])


1970
K. J. Åström established the importance of digital controls in process applications. ([218], [219])


1970’s
H. H. Rosenbrock ([190]) , A. G. J. MacFarlane and I. Postlethwaite ([189]) initiated a great deal of activity to extend classical frequency-domain techniques and the root locus to multivariable systems.


1976
D. Youla, H. Jabr, and J. Bongiorno introduced the parameterization of all stabilizing controllers for a particular system in a very effective manner. ([184], [185])


1981
J. Doyle and G. Stein ([188]) , M. G. Safonov, A. J. Laub, and G. L. Hartmann ([188]) showed the importance of the singular value plots versus frequency in robust multivariable design. Using these plots, many of the classical frequency-domain techniques can be incorporated into modern design.


1986
M. Athans pursued the importance of the singular value plots versus frequency in robust multivariable design in aircraft and process control. ([186])

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Adaptive Control
Mid-1950’s
Significant growth of interests in adaptive control with flight control a major driving force ([63]).


1950’s
The idea to ignore uncertainty and treat estimates as true values is the so-called certainty equivalence principle ([72]). See [97] for a discussion on the relationship between the separation principle and the certainty equivalence principle. It should be mentioned that the certainty equivalence principle was discussed in the economics literature in the late 50’s ([98]).


1951
A self-optimizing controller was proposed for driving a combustion engine under optimal conditions toward optimal working conditions, and the design was successfully flight tested ([71]). This ushered in a new era in the field of control.


1957-1961
A major step forward in the direction of formulating optimization problems to obtain adaptive controllers was taken by the development of dynamic programming [73]. The application of such methods to adaptive control is discussed in [74].


1958
The model reference adaptive control was introduced and used to solve the flight control problems ([64], [65]).


1965
Experiments and simulations of model reference adaptive control indicated that there could be problems with instability specifically if the adaptive gain was too large. The stability issues of such systems were first approached using Lyapunov theory ([66]).


1966
In attempts to replace the MIT-rule by other parameter adjustment rules which ensured stability, it was shown in [67] that one could achieve stability if all state variables were measured.


1970’s-80’s
Much work on the self-tuning regulator was carried out in the 1970's and 1980’s, e.g. see [70].


1980
The solution to the flight control problem was given by gain scheduling not by adaptive control ([68]).


1980
Process control was instrumental in the development of a self-tuning regulator which was first proposed in ([69]).


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Filtering and Stochastic Control
A comprehensive survey of linear filtering theory can be found in [75].
1950
H. W. Bode and C. E. Shannon proposed the solution to the problem of prediction and smoothing ([76]). A modern account of the solution can be found in [77] and more detailed treatment of the ideas are presented in [78] [79].


1960
R. E. Kalman ([81],[82],[83]) made explicit that an effective solution to the Wiener-Hopf equation using method of spectral factorization ([80]) could be obtained when the continuous process had a rational spectral density.
Stratanovich derived the conditional density equation using the so-called Stratanovich calculus ([111]).


1960-63
The theory of optimal stochastic control in the fully observable case is quite similar to that of non-linear filtering in connection with the linear quadratic stochastic control problem ([79]). Early works in this area are due to Howard ([121]), Florentin ([91]), and Fleming ([122]); See also [123].


1960-64
Inspired by the development of Dynamic Programming by Bellman ([85]) and the ideas of Caratheodory ([86]) related to Hamilton-Jacobi Theory, the development of optimal control of nonlinear dynamical systems took place ([87], [88]), see [89], [84], [90] for further details of the ideas.


1961-1973
The solution to quadratic cost optimal control for linear stochastic dynamical systems was provided by Florentin ([91], [92]), by Joseph in discrete-time ([93]), and by Kushner ([94]). The definitive treatment of the problem was proposed by Wonham ([95]), see also [96].


1962
The partially observable stochastic control problem treated by Florentin ([92]), Davis and Varayia ([125]) and Fleming and Pardouz ([126]). Detailed discussions can be found in [127] and the references therein.


1964
For a good discussion on the distinction between open-loop stochastic control and feedback control see [99].


1965
Non-linear filters are almost always infinite dimensional and there are only a few known examples where the filter is known to be a finite dimension. The Kalman filter is an example and the other finite-state cases are first discussed in [104] [114] and also [112] [113].


1967-79
A difficulty is that one of the fundamental equations of non-linear filtering turns out to be a non-linear stochastic partial differential equation ([79]). Zakai ([105]), Duncan ([106]), and Mortensen ([107]) proposed alternative solutions to the above difficulty which involves a linear stochastic differential equation.


1971
Giransov introduced the idea of measure transformation in stochastic differential equation, see [79], [110], [115] and the references therein for details.


1971-72
The earlier ideas of nonlinear filtering were developed and introduced by Forest and Kailath ([100]), and in definitive form by Fujisaki, Kallianpur, Kunita ([101]).


1976
Bobrovsky and Zakai proposed a method for obtaining lower bounds on the mean-squared error ([119]).


1978
As an attempt to address some of the issues with non-linear filtering, pathwise non-linear filtering was considered where the filter depends continuously on the output ([117], [118]).


1996
The Linear Quadratic Gaussian methodology and optimal non-linear stochastic control have found a wide variety of applications in aerospace, multi-variable control design systems, finance, etc. ([115], [128]).


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H-Infinity Control
1970’s
Robust Control aimed to blend the best of the classical methods of the 1940—50’s with the more sophisticated modern theory of the 1960—70’s ([27]).


1976-1981
G. Zames introduced the theory of H-infinity control. He formulated a basic feedback problem as an optimization problem with an operator norm, in particular, an H-infinity norm ([34], [35], [36]).
Related contemporaneous works in the theory of H-infinity control are those of J.W. Helton ([37]) and A. Tannenbaum ([38]).


1981
The input-output mapping for a standard feedback system ([27]) has four transfer functions and it is said to be internally stable if these four transfer functions are all in H-infinity. Internal stability is robust if it is preserved under perturbation of the plant model. J.C. Doyle and G. Stein showed that internal stability is preserved under special perturbations ([39]). This led to the robust stability design problem.
G. Zames postulated that measuring performance in terms of the infinity-norm rather than the traditional 2-norm (LQG) might be much closer to the practical needs. This ushered in the era of H-infinity optimal control. The H-infinity control problem synthesizes a controller which guarantees the stability of the closed-loop and minimizes the L2 induced gain from exogenous inputs to regulated outputs ([27], [33]).


1981-1992
Relations between H-infinity and many other topics can be found in areas like Risk Sensitive Control (P. Whittle) ([56], [57]); Differential Games (T. Bagar, P. Bernhard, M. D. J. Limebeer, B. D. O. Anderson, P. P. Khargonekar, M. Green) ([33], [58], [60]); J-lossless Factorization (M. Green) ([59]); Maximum Entropy methods (H. Dym and I. Gohberg) ([61], [62]).


1982
John C. Doyle argued that model uncertainty is often described very effectively in terms of norm-bounded perturbations. For these perturbations and the H-infinity performance objective he developed a powerful tool, the structured singular value, for testing robust stability ([42], [43]).


1984
John C. Doyle presented the 1st solution to a general MIMO H-infinity optimal control problem ([47]), which relies on state-space methods.
K. Glover tackled the problem of model reduction and presented the solution using Hankel norm of an error, and an explicit algorithm was given for state-space LTI systems ([48]).


1987
B. A. Francis and J. C. Doyle presented a summary of the theory of H-infinity Control in [40].
B. A. Francis gave a detailed treatment of the theory of H-infinity Control in [41]. He developed an operator-theoretic approach to the H-infinity control problem.
B. A. Francis and John C. Doyle gave a modified solution to the general rational MIMO H-infinity optimal problem but suffered from the high order of the Riccati equations ([49], [50]).


1988
D. J. N. Limebeer, G. D. Halikias and Y. S. Hung showed that a subsequent minimal realization of the controller has state dimension no greater than that of the plant. This suggested the likely existence of similarly low dimension optimal controllers in the general two-by-two case ([50], [51], [52]).
Simple state space H-infinity controller formulae were first announced by K. Glover and J. Doyle ([53]) .


1988-1990
P. P. Khargonekar, I. R. Petersen, M. A. Rotea, and K. Zhou showed that for the state feedback H-infinity problem one can choose a constant gain as a sub-optimal controller, and a formula for the state-feedback gain matrix was given in terms of an algebraic Riccati equation. They also established connections between H-infinity optimal control, quadratic stabilization, and linear-quadratic differential games and showed that the state-feedback H-infinity problem can be solved by solving an algebraic Riccati equation and completing the square ([54], [55]).


1989
John C. Doyle, K. Glover, Khargonekar, B. A. Francis developed state-space procedures for solving H-infinity problem ([32]).
K. Glover and D. C. McFarlane introduced the H-infinity loop-shaping design method which provides systematic procedures for obtaining sensible controllers that meet performance objectives and guarantee robustness against model uncertainty and unmeasured disturbances ([27], [29], [31]).
Most of the solution techniques for the H-infinity control problem were in an input-output setting and involved analytic functions (Nevanlinna-Pick interpolation ([27])) or operator theoretic methods ([44], [45], [46]).


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Linear Matrix Inequality (LMI)
1890
A. M. Lyapunov published his seminal work known as Lyapunov theory ([1]). This is usually referred to as the first appearance of the Linear Matrix Inequality (LMI) in control theory; analytical solution of the Lyapunov LMI via Lyapunov equation.


1940’s
A. I. Lur’e and V. N. Postnikov were first to apply Lyapunov’s methods to some specific practical problems in control engineering, specifically the problem of stability of a control system with nonlinearity in the actuator. Small LMIs were solved by hand ([2], [3]).


Early 1960’s
R. E. Kalman, V. A. Yakubovich and V. M. Popov managed to reduce the solution of the LMIs that arose in the problem of Lur’e to simple graphical criteria known as Kalman-Yakubovich-Popov (KYP) lemma ([4], [5], [6]).


1964
The KYP lemma resulted in Popov criterion, Circle criterion, Tsypkin criterion ([7], [8]) and many variations.


1962-1965
V. A. Yakubovich published many papers ([6], [9], [10]) highlighting the important role of LMIs in control theory; e.g. The solution of certain inequalities in automatic control theory (1962) and The method of matrix equalities in the stability theory of nonlinear control systems (1965).


Late 1960’s
The Kalman-Yakubovich-Popov (KYP) lemma and extensions were extensively studied and found to be related to the idea of passivity, the small gain criteria introduced by Zames ([11], [12]) and Sandberg ([13], [14], [15]) and quadratic optimal control .


1965
The idea of having a computer search for a Lyapunov function appeared in the literature.


1970
By then, it was known that LMI appearing in the KYP lemma could also be solved by solving a certain algebraic Riccati equation ([16]).


Early 1970’s
B. D. O. Anderson and S. Vongpanitlerd noted the difficulty in solving the LMI directly ([17]).


1971
J. C. Willems in a paper on Quadratic Optimal Control pointed out that an LMI problem could be solved by studying the symmetric solutions of a certain Riccati equation ([19]).


1976
H. P. Horisberger and P. R. Belanger observed that the existence of a quadratic Lyapunov function that simultaneously proves stability of a collection of linear systems is a convex problem involving LMIs ([22]).


1982-1983
E. S. Pyantnitskii and V. I. Skorodinskii were perhaps the first to assert that many LMIs that arise in control and systems theory can be formulated as convex optimization problems which can be reliably solved by computer solutions for which no analytical solution was likely to be found. They were the first to formulate the search for a Lyapunov function as a convex optimization problem, and then apply an algorithm guaranteed to solve the optimization problem ([20], [21]).


1984
N. Karmarkar introduced a new linear programming algorithm that solved linear programs in polynomial-time, like the ellipsoid method, but in contrast to the ellipsoid method, was also very efficient in practice ([24]).


1988
Yu. Nesterov and A. Nemirovski developed interior-point methods that apply directly to convex problems involving matrix inequalities, and in particular, to the problems encountered in control theory ([25]).


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Nonlinear Control
1883-1892
Lindstedt ([129]) and Poincare ([130]) tackled the problem of finding a limit cycle solution for some of the second-order nonlinear differential equations.


1892
Poincare ([130]) introduced the phase plane method in studying the second-order nonlinear differential equations. This method became the dominant approach and a valuable tool available to control engineers from the late 1930’s.
Following Poincare, many contributions were made to the field of phase plane topology such as information on singular points and the structure of trajectories near them, and conditions for the existence of limit cycles ([134]).


1915
Stability theory for linear differential equations was established around the work of Poincare but little was done on the general nonlinear differential equations case as Lyapunov's original work was neglected ([135]).
Major research efforts into the effects of nonlinearity in control systems was carried out at MIT as Bush and his colleagues studied nonlinear differential equations considering differential analyzers using mechanical integrators. These efforts included implementation of various designs by Hazen including some using relays being aware of the limitations on the performance due to backlash in gears ([136]).
Motivated by wartime, the need for accurate fire control systems led to significant work on servomechanism in the western world. The phase plane methods and describing function approach were being used to study the nonlinear effects ([136]).


1918
Continuing Duffing's seminal work ([133]), various forms of harmonic balance technique were used to study both free and forced oscillations in the second-order nonlinear differential equations ([176]).


1941
Minorsky ([137]) made a brief reference to nonlinear control problems and the possibility of using Lyapunov’s method.


1949-1958
In studying relay systems, it was realized that the output from a relay, once it had switched, became independent of the input which led Hamel ([170]) and Tsypkin ([171]) to develop techniques for accurate measurement of the limit cycle in such systems. Further details can be found in [168], [169], [172].


1949-1958
For detailed discussions on this topic and latest developments in nonlinear control see [177], [178], [179], [180], [181], [182], [183].


1950’s
Phase plane technique was the main focus in studying the nonlinear differential equations with many papers and books appearing during this year ([138], [139], [140], [141], [142]). However, different nonlinear effects in specific second-order systems were investigated and understood later; nonlinear effects like the effects of torque saturation, nonlinearities in the error channel, backlash, friction, and relay control in second-order systems, optimum control using relays, chattering in relay systems. Detailed coverage of these developments were published, see e.g. [143], [144], [145], [146], [147].
Goldfarb, Dutilh, Oppelt, Kochenburger and Daniell appeared to have independently used the describing function in studying nonlinear differential equations ([148]). The method is identical to a harmonic balance approach, where the first harmonic only is balanced, but was developed in a way more suitable for use in feedback control, in which nonlinear systems were modeled in terms of interconnected blocks of static nonlinear and transfer function elements ([176]).


1954
The problem of examining nonlinear systems with random inputs was first pioneered by Booton ([160]) who approximated the nonlinearity by a linear gain such that the error between the nonlinearity output and that from the linear gain with the same random input (Gaussian) was minimum. Other related materials and contributions can be found in ([161], [162], [164], [165]).


1954-1955
The extension of the describing function theory to determine the stability of any predicted limit cycle ([150]) and to utilize the describing function to determine the forced harmonic response of a nonlinear system ([151], [152]).


1956
In attempts to study the occurrence of nonlinear phenomena in control loops by extending the describing function, particularly servomechanism, West et al. ([156]) realized that the response of nonlinear elements to two harmonic inputs had to be examined.


1956-58
To avoid limit cycles predicted by the describing function method, a common procedure was to change the open-loop dynamics so that no intersection existed between the loci of the system and the specialized describing function on the Nyquist diagram ([176]). Other alternatives either placed nonlinearity in series or parallel with the inherent system or used nonlinear integrators for specific problems ([154], [155]).


1957-58
The incremental describing function was used to assess the stability of a limit cycle ([157], [158]).


1962-1943
Van der Pol ([131], [132]) and Krylov and Bogoliubov ([132]) introduced averaging methods for obtaining solutions to the second-order nonlinear differential equations.


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References
[1] M. Lyapunov. Probleme general de la stabilite du mouvement, volume 17 of Annals of Mathematics Studies. Princeton University Press, Princeton, 1947.

[2] I. Lur'e and V. N. Postnikov. On the theory of stability of control systems. Applied mathematics and mechanics, 8(3), 1944. In Russian.

[3] I. Lur'e. Some Nonlinear Problems in the Theory of Automatic Control. H. M. Stationery Off., London, 1957. In Russian, 1951.

[4] R. E. Kalman. Lyapunov functions for the problem of Lur'e in automatic control. Proceedings of National Academy of Sciences., USA, 49:201-205, 1963.

[5] V. M. Popov. Absolute stability of nonlinear systems of automatic control. Automation and Remote Control, 22:857-875, 1962.

[6] V. A. Yakubovich. The solution of certain matrix inequalities in automatic control theory. Soviet Math. Doklady, 3:620-623, 1962. In Russian, 1961.

[7] Ya. A. Tsypkin. Frequency criteria for the absolute stability of nonlinear sampled data systems. Automatic Remote Control, 25:261-267, 1964.

[8] Ya. Z. Tsypkin. A criterion for absolute stability of automatic pulse systems with monotonic characteristics of the nonlinear element. Soviet PhY8. Doklady, 9:263-266, 1964.

[9] V. A. Yakubovich. Solution of certain matrix inequalities encountered in nonlinear control theory. Soviet Math. Dokl., 5:652-656, 1964.

[10] V. A. Yakubovich. The method of matrix inequalities in the stability theory of nonlinear control systems, I, II, Ill. Automation and Remote Control, 25-26(4):905-917,577-592,753-763, April 1967.

[11] G. Zames. On the input-output stability of time-varying nonlinear feedback systems-Part I: Conditions derived using concepts of loop gain, conicity, and positivity. IEEE Transactions on Automatic Control, AC-11:228-238, April 1966.

[12] G. Zames. On the input-output stability of time-varying nonlinear feedback systems-Part II: Conditions involving circles in the frequency plane and sector nonlinearities. IEEE Transactions on Automatic Control, AC-11:465-476, July 1966.

[13] I. W. Sandberg. A frequency-domain condition for the stability of feedback systems containing a single time-varying nonlinear element. Bell Systems Technology Journal, 43(3):1601-1608, July 1964.

[14] W. Sandberg. On the boundedness of solutions of non-linear integral equations. Bell Systems Technology Journal, 44:439-453, 1965.

[15] W. Sandberg. Some results in the theory of physical systems governed by nonlinear functional equations. Bell Systems Technology Journal, 44:871-898, 1965.

[16] S. Boyd and E. Feron and V. Balakrishnan and L. El Ghaoui. History of linear matrix inequalities in control theory. In Proceedings of American Control Conference, pp. 31-34, 1994.

[17] D. O. Anderson and S. Vongpanitlerd. Network analysis and synthesis: a modern systems theory approach. Prentice-Hall, 1973.

[18] J. C. Willems. Least squares stationary optimal control and the algebraic Riccati equation. IEEE Transactions on Automatic Control, AC-16(6):621-634, December 1971.

[19] V. A. Yakubovich. Dichotomy and absolute stability of nonlinear systems with periodically non-stationary linear part. Systems and Control Letters, 1988.

[20] E. S. Pyatnitskii and V. I. Skorodinskii. Numerical methods of Lyapunov function construction and their application to the absolute stability problem. Systems and Control Letters, 2(2):130-135, August 1982.

[21] E. S. Pyatnitskii and V. I. Skorodinskii. Numerical method of construction of Lyapunov functions and absolute stability criteria in the form of numerical procedures. Automation and Remote Control 44(11):1427-1437, 1983.

[22] H. P. Horisberger and P. R. Belanger. Regulators for linear, time invariant plants with uncertain parameters. IEEE Transactions on Automatic Control, AC-21:705-708,1976.

[23] G. Schultz, F. T. Smith, H. C. Hsieh, and C. D. Johnson. The generation of Lyapunov functions. In C. T. Leonde, editor, Advances in Control Systems, volume 2, pages 1-64. Academic Press, New York, 1965.

[24] N. Karmarkar. A new polynomial-time algorithm for linear programming. Combinatorica, 4(4):373-395, 1984.

[25] Yu. Nesterov and A. Nemirovsky. Interior point polynomial methods in convex programming: Theory and application. SIAM, 1993.

[26] F. L. Lewis, Introduction to Modern Control Theory, Prentice-Hall, 1992.

[27] K. Zhou, J. C. Doyle and K. Glover, Robust and Optimal Control, Prentice-Hall, 1996.

[28] J. C. Doyle, B. A. Francis and A. R. Tannenbaum, Feedback Control Theory, Macmillan, 1992.

[29] K. Glover, D. McFarlane, "Robust stabilization of normalized coprime factor plant descriptions with H-infinity bounded uncertainty", IEEE Transactions on Automatic Control, 34 (1989), 821-830.

[30] McFarlane, D.C., and K. Glover, "A Loop Shaping Design Procedure using Synthesis," IEEE Transactions on Automatic Control, vol. 37, no. 6, pp. 759- 769, June 1992.

[31] D. C. McFarlane and K. Glover, Robust Controller Design Using Normalized Coprime Factor Plant Descriptions, Lecture Notes in Control and Information Science, No. 138, Springer-Verlag, Berlin, 1989.

[32] J. Doyle, K. Glover, P. Khargonekar, and B. Francis, "State-space solutions to standard H2 and H-infinty control problems," IEEE Transactions on Automatic Control, vol. 34, pp. 831--846, Aug. 1989.

[33] M. Green and D. J. N. Limebeer, Linear Robust Control. Englewood Cliffs, NJ: Prentice-Hall, 1995.

[34] G. Zames, "Feedback and complexity, Special plenary lecture addendum" , IEEE Conf. Decision Control , 1976.

[35] G. Zames, "Optimal sensitivity and feedback: weighted seminorms, approximate inverses, and plant invariant schemes" , Proc. Allerton Conf. , 1979.

[36] G. Zames, "Feedback and optimal sensitivity: model reference transformations, multiplicative seminorms, and approximate inverses" IEEE Transactions on Automatic Control, AC-26, 1981, pp. 301–320.

[37] J. W. Helton, "Operator theory and broadband matching", Proc. Allerton Conf. , IEEE,1979.

[38] A. Tannenbaum, "On the blending problem and parameter uncertainty in control theory", Technical Report Dept. Math. Weizmann Institute, 1977.

[39] J. C. Doyle, G. Stein, "Multivariable feedback design: concepts for a classical modern synthesis", IEEE Transactions on Automatic Control , AC-26, 1981, pp. 4–16.

[40] B. A. Francis, J. C. Doyle, "Linear control theory with an H-infinity optimality criterion", SIAM J. Control and Opt., 25, 1987, pp. 815–844.

[41] B.A. Francis, "A course in H-infinity control theory", Lecture Notes in Control and Information Science, 88, Springer, 1987.

[42] Packard, A.K., M. Fan and J. Doyle, "A power method for the structured singular value," Proc. of IEEE Conference on Control and Decision, December 1988, pp. 2132-2137.

[43] J. Doyle. Analysis of feedback systems with structured uncertainties. Proc. IEE, 129:242-- 250, 1982.

[44] D. Sarason, Generalized Interpolation in H-infinity, Transactions of the American. Math. Society 127 (1967), 179-203.

[45] V.M. Adamjan, D.Z. Arov, and M.G. Krein, Infinite block Hankel matrices and related extension problems, Transactions of the American Math. Society, 111: 133-156, 1978.

[46] J. A. Ball and J. W. Helton. A Beurling-Lax theorem for the Lie group U(m,n) which contains most classical interpolation theory. Journal of Operator Theory, 9:107-142, 1983.

[47] J. C., Doyle, Lecture Notes in Advances in Multivariable Control, ONR/Honeywell Workshop, Minneapolis, MN, 1984.

[48] K. Glover. All optimal Hankel-norm approximations of linear multivariable systems and their L-infinity error bounds. International Journal of Control, 39:1115-1193, 1984.

[49] B. A. Francis, A course in H-infinity control theory, Lecture Notes in Control and Information Sciences, vol. 88, 1987.

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Inilah Islam dan Seruan Islam

Oleh: Syaikh Muqbil bin Hadi

1. Kita beriman kepada Allah, nama-nama-Nya dan sifat-sifat-Nya, menurut apa yang terdapat dalam Al-Qur’an dan As-Sunnah, tanpa tahrif(menyimpangkan maknanya), mentamtsil (memisalkan dengan makhluk), mentasybih(menyerupakan dengan makhluk) dan tanpa menta’thil (meniadakan atau menghapus sifat itu dari Allah)

2. Kita berkeyakinan bahwa berdo’a kepada orang mati, meminta tolong kepada mereka dan begitu juga terhadap orang yang masih hidup pada masalah yang tidak disanggupi kecuali oleh Allah adalah syirik. Begitu juga keyakinan terhadap jimat-jimat, bahwa dia bisa memberikan manfaat bersama Allah atau tanpa Allah adalah syirik. Dan membawanya tanpa keyakinan adalah khurofat

3. Kita berpegang dengan dhazir ayat dan Sunnah. Kita tidak menta’wilkannya kecuali ada dalil yang membolehkan untuk melakukan itu dari Al-Qur’an dan Sunnah

4. Kita beriman behwa kaum mukminin akan melihat Rabb mereka pada Hari Akhir tanpa mentakyif (menanyakan bagaimana). Dan kita beriman dengan syafa’at dan akan dikeluarkannya orang-orang yang bertauhid dari neraka

5. Kita mencintai para Sahabat Rasulullah shallallahu alaihi wa sallam dan membenci orang-orang yang mencela mereka. Kita meyakini bahwa menghina mereka berarti menghina agama ini. Karena merekalah yang membawanya kepada kita. Kita mencintai Ahlul Bait Nabi dengan kecintaan yang berdasar syariat

6. Kita mencintai Ahlul Hadits dan seluruh para salaf (pendahulu) ummat ini dari kalangan Ahlus Sunnah

7. Kita membenci Ilmu Kalam. Dan kita berkeyakinan bahwa dialah penyebab terbesar perpecahan ummat ini.

8. Kita tidak menerima keterangan dari kitab-kitab fiqih, tafsir, cerita-cerita lampau dari sejarah Nabi shallallahu alaihi wa sallam, kecuali yang ditetapkan Allah dan Rasul-Nya. Bukan berarti kita membuangnya dan tidak butuh kepadanya, tetapi kita mengambilnya dari kesimpulan para ulama kita yang faham dan yang selain mereka. Dan kita tidak menerima hukum kecuali yang berdasarkan argumen yang shahih

9. Kita tidak menulis dalam kitab-kitab dan pelajaran-pelajaran kita serta kita tidak berkhutbah kecuali dengan Al-Qur’an atau Hadits yang shahih untuk berhujjah. Kita membenci apa yang terdapat dalam kebanyakan kitab-kitab para pemberi nasehat, yaitu cerita-cerita bohong dan hadits-hadits lemah, bahkan palsu.

10. Kita tidak mengkafirkan seorang muslim kecuali karena kesyirikan atau karena meninggalkan shalat atau murtad. Semoga Allah melindungi kita dari hal-hal itu

11. Kita beriman bahwa Al-Qur’an adalah Kalamullah (ucapan Allah), bukan makhluk

12. Kita berpendapat wajib saling tolong-menolong sesama muslim mana saja dalam kebenaran. Dan kita berlepas diri dari dakwah-dakwah jahiliyah

13. Kita berpendapat tidak boleh memberontak terhadap pemerintah kaum muslimin selama mereka masih muslim. Kita tidak berpendapat bahwa revolusi adalah cara yang membawa kebaikan, bahkan itu adalah cara yang merusak masyarakat. Adapun sikap kita terhadap penguasa ‘Aden (Penguasa yg berhaluan komunis/sosialis), maka kita berpendapat bahwa memerangi mereka adalah adalah wajib hingga mereka mau bertaubat dari penyelewengannya, yaitu sosialisme dan mengajak manusia untuk beribadah kepada Lenin, Karl Mark dan tokoh-tokoh kafir lainnya

14. Kita berpendapat bahwa jama’ah-jama’ah yang baru dan banyak sekarang ini adalah penyebab perpecahan kaum muslimin dan yang melemahkan mereka

15. Kita berpendapat bahwa dakwah Ikhwanul Muslimin tidak cocok dan tidak baik untuk perbaikan masyarakat, karena mereka adalah dakwah politik, bukan dakwah yang bertujuan untuk memperbaiki jiwa. Dan dia juga dakwah bid’ah, karena dia adalah dakwah untuk membai’at orang-orang bodoh. Dan dakwah Ikhwanul Muslimin juga adalah dakwah fitnah, karena berdiri dan berjalan diatas kebodohan

Kita menasehati sebagian teman-teman kita yang masih bekerja didalamnya agar mereka segera meninggalkannya, hingga dengan itu dia tidak menyia-nyiakan waktunya pada masalah yang tidak bermanfaat bagi Islam dan kaum muslimin. Dan wajib bagi setiap muslim meyakini bahwa Allah akan menolong Islam dan kaum muslimin melalui tangan muslim mana saja dan jama’ah mana saja.

16. Adapun tentang Jama’ah Tabligh, silakan Anda membaca penuturan Syaikh Muhammad bin Abdul Wahhab Al Washshabi, beliau berkata:
(a). Mereka mengamalkan hadits-hadits dhaif (lemah), maudhu’ (palsu) dan yang tidak ada asalnya
(b). Tauhid mereka penuh dengan bid’ah, bahkan dakwah mereka berdasarkan bid’ah, karena dakwah mereka dasarnya adalah Al-Faqra yaitu khuruj (keluar). Dan ini diharuskan setiap bulan 3 hari. Setiap tahun 40 hari dan seumur hidup 4 bulan. Setiap minggu ada 2 Jaulah…Jaulah pertama di masjid yang didirikan shalat padanya. Dan yang kedua berpindah-pindah. Disetiap hari ada 2 halaqah, halaqah pertama di masjid yang didirikan shalat padanya. Yang kedua di rumah. Mereka tidak senang terhadap seseorang kecuali bila ia mengikuti mereka. Tidak diragukan lagi bahwa ini adalah bid’ah dalam agama yang tidak diperbolehkan oleh Allah
(c). Mereka berpendapat bahwa dakwah kepada tauhid itu memecah belah
(d). Mereka berpendapat bahwa mengajak manusia kepada sunnah itu memecah belah ummat
(e). Pemimpin mereka berkata dengan tegas bahwa: bid’ah yang bisa mengumpulkan manusia lebih baik daripada Sunnah yang memecah belah manusia
(f). Mereka menyuruh manusia untuk tidak menuntut ilmu yang bermanfaat secara halus atau terang-terangan
(g). Mereka berpendapat bahwa manusia tidak bisa selamat kecuali dengan cara mereka. Dan mereka membuat permisalan dengan perahu Nabi Nuh ‘alaihis salam, siapa yang naik akan selamat dan siapa yang tidak naik akan hancur. Mereka berkata:”Sesungguhnya dakwah kita seperti perahu Nabi Nuh”. Saya sendiri yang mendengarkannya di Urdun dan Yaman
(h). Mereka tidak menaruh perhatian terhadap Tauhid Uluhiyah dan Tauhid Asma wa Sifat
(i). Mereka tidak mau menuntut ilmu dan berpendapat bahwa waktu yang digunakan untuk menuntut ilmu hanya sia-sia belaka

17. Kita mengikat pemahaman kita dengan Al-Qur’an dan Sunnah Rasulullah shalallahu ‘alaihi wasallam yang berdasarkan pemahaman Salaf (pendahulu) ummat ini dari kalangan ahli hadits tanpa fanatik terhadap individu mereka, tetapi kita mengambil kebenaran dari orang yang membawanya. Kita tahu ada orang yang mengaku-ngaku sebagai Salafi (pengikut Salaf), padahal Salaf berlepas tangan dengan mereka, sebab dia berteman dengan orang-orang yang menghalalkan apa yang diharamkan Allah

18. Kita berkeyakinan bahwa politik adalah bagian dari agama ini. Dan orang-orang yang memisahkan antara agama dan politik berarti ingin menghancurkan Dien (agama) ini dan ingin menyebarkan kekacauan seperti yang terjadi disebagian negeri kaum muslimin. Mereka mengatakan “Agama untuk Allah dan negara untuk bersama”. Ini adalah slogan-slogan jahiliyah

19. Kita berkeyakinan bahwa tidak ada izzah (kemuliaan) dan pertolongan bagi kaum muslimin, hingga mereka mau kembali kepada Kitabullah dan Sunnah Rasulullah shalallahu ‘alaihi wasallam

20. Kita membenci kelompok-kelompok baru: Komunisme, Ba’tsi, Nashiry, Sosialisme, dan Rafidhah yang telah keluar dari Islam. Kita berpendapat bahwa manusia sekarang menjadi 2 golongan, yaitu golongan Hizbur Rahman (kelompok Allah), yaitu orang-orang yang melaksanakan rukun-rukun Islam dan Iman tanpa menolak sedikitpun syariat Allah, dan Hizbusysyaithan (kelompok setan), yaitu yang memerangi syariat-syariat Allah

21. Kita mengingkari orang yang membagi agama menjadi “kulit” dan “inti”. Dan ini adalah dakwah yang menghancurkan

22. Kita mengingkari orang yang merasa tidak butuh kepada ilmu Sunnah dan mengatakan “Ini bukan waktu mempelajarinya”. Beginilah orang yang enggan mengamalkan Sunnah Rasulullah shalallahu ‘alaihi wasallam

23. Kita berpendapat handaknya kita mendahulukan yang paling penting dari yang penting. Maka wajib bagi seorang muslim untuk bersungguh-sungguh memperbaiki aqidah, kemudian membinasakan komunisme dan Ba’tsiyyah dan itu bisa tercapai dengan persatuan yang berdasarkan Al-Qur’an dan Sunnah

24. Kita berpendapat bahwa jama’ah yang merangkul Rafidhah, Syi’ah, Sufi, dan Sunni tidak bisa menghadapi musuh karena itu tidak akan tercapai kecuali dengan ukuwwah (persaudaraan) yang jujur dan persatuan dalam aqidah

25. Kita mengingkari orang yang berkata dan menyangka bahwa para da’i yang mengajak manusia kembali kepada Allah adalah orang-orang Wahhabi. Kita tahu bahwa mereka memiliki maksud yang sangat jijik dan kotor yaitu ingin memisahkan para ulama dengan masyarakatnya

26. Dakwah kita dan aqidah kita lebih kita cintai dari diri-diri, harta-harta dan anak-anak kita. Kita tidak akan rela menjualnya dengan emas dan uang…Kita suarakan terus dakwah ini sampai pupus harapan orang yang ingin memperalat dakwah ini. Dia mengira dia bisa mendikte kita dengan uang dan harta. Oleh sebab ini, mereka menjadi putus asa untuk membujuk kita dengan harta dan kedudukan

27. Kita membenci pemerintah-pemerintah yang ada, sekedar (sesuai dengan) kejahatan yang mereka lakukan dan kita mencintai sekedar (sesuai dengan) kebaikan yang ada padanya. Kita tidak boleh memberontak kecuali bila kita telah melihat adanya kekafiran yang jelas pada pemerintahan-pemerintahan itu berdasarkan burhan (bukti nyata) dari Allah

Pemerintah yang paling kita benci sekarang adalah pemerintahan ’Aden yang berhaluan komunis lagi Atheis, semoga Allah segera membinasakannya dan menyucikan negeri-negeri Islam darinya

28. Kita menerima bimbingan dan nasehat dari siapa saja, karena kita adalah para penuntut ilmu yang bisa benar dan salah

29. Kita mencintai Ulama Sunnah yang hidup sekarang. Dan kita ingin mengambil faedah dari mereka. Dan kita merasa sedih karena kejumudan sebagian mereka

30. Kita tidak menerima fatwa kecuali berdasarkan Al-Qur’an dan Sunnah Rasulullah shalallahu ‘alaihi wasallam yang tsabit (kokoh)

31. Kita mengingkari kepada pihak-pihak yang bertanggung jawab dan sektor lainnya dengan adanya usaha mengunjungi kuburan Lenin dan tokoh-tokoh sesat lainnya untuk menghormati mereka

32. Kita mengingkari pemerintah muslim yang melakukan kerja sama dengan musuh-musuh Islam, baik itu antek-antek Amerika atau komunis

33. Kira mengingkari dakwah-dakwah jahiliyah seperti kesukuan dan fanatisme Arab. Kita menggolongkannya sebagai dakwah-dakwah jahiliyah dan termasuk sebab yang memundurkan umat Islam

34. Kita menunggu seorang mujaddid yang Allah akan memperbaharui agama ini melaluinya. Ini berdasarkan hadits yang diriwayatkan Abu Daud dalam sunannya dari Abu Hurairah radhiyallahu’anhu dari Nabi shalallahu ‘alaihi wasallam:”Sesungguhnya Allah akan membangkitkan bagi umat ini disetiap 100 tahun orang yang akan memperbaharui untuk mereka agama mereka” Dan kita berharap agar kebangkitan Islam menjadi mudah karenanya

35. Kita berkeyakinan bahwa orang yang mengingkari hadits tentang Al-Mahdi dan Dajjal serta turunnya Isa bin Maryam adalah sesat. Dan bukan yang kita maksudkan imam Mahdi dari kalangan Rafidhah, akan tetapi dari Ahlul bait Nabi yang tergolong Ahlus Sunnah. Dia akan memenuhi bumi dengan keadilan sebagaimana sebelumnya bumi ini telah dipenuhi dengan kezaliman. Kita katakan “yang tergolong Ahlus Sunnah”, karena orang yang mencela Sahabat tidak dianggap adil

36. Ini sekilas tentang aqidah dan dakwah kita. Kalau disebut dengan dalil akan memperpanjang kitab ini. Dan telah kusebut dengan panjang lebar dalam kitab “Al-Makhraj minal Fitnah”. Dan siapa yang memiliki keyakinan yang sebaliknya dari yang telah kita sebutkan ini, maka kami bersedia menerima nasehat jika dia benar dan kami bersedia berdebat jika dia salah serta berpaling darinya jika dia membangkang

Ini yang perlu kita ketahui. Dan ini bukan seluruh dakwah dan aqidah kita, karena dakwah kita berdasarkan Al-Qur’an dan Sunnah dan mengajak kepada Al-Qur’an dan Sunnah. Demikianlah aqidah ini. Cukup Allah bagi kita dan Dia adalah sebaik-baik tempat bertawakal. Tidak ada daya dan kekuatan kecuali dengan izin Allah. (Diambil dari kitab “Hadzihi Da’watuna wa ‘Aqidatuna hal 11-23 dan dialih bahasakan oleh Mummad ‘Ali ‘Ishmah Al-Medani)

(Diambil dari Buletin Al-Manhaj, edisi 7/1419 H/1999 M, yang diterbitkan oleh Lajnah Khidmatus Sunnah wa Muharobatul Bid’ah. Ponpes Ihyaus Sunnah. Degolan-Yogyakarta)

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Perlindungan Jiwa dan Harta

Allah azza wa jalla berfirman يَا أَيُّهَا الَّذِينَ آمَنُوا لا تَأْكُلُوا أَمْوَالَكُمْ بَيْنَكُمْ بِالْبَاطِلِ إِلا أَنْ تَكُونَ تِجَارَةً عَنْ تَرَاضٍ مِنْكُمْ وَلا تَقْتُلُوا أَنْفُسَكُمْ إِنَّ اللَّهَ كَانَ بِكُمْ رَحِيمًا “Hai orang-orang yang beriman, janganlah kamu saling memakan harta sesamamu dengan jalan yang batil, kecuali dengan jalan perniagaan yang berlaku dengan suka sama-suka di antara kamu. dan janganlah kamu membunuh dirimu; Sesungguhnya Allah adalah Maha Penyayang kepadamu.” (Q.S. An-Nisaa:29)

Agama Islam mengakui dan melindungi hak milik perseorangan, asal diperolehnya dengan jalan yang halal. Sebab itu, diperintahkan kepa Publish Post da orang-orang beriman, supaya jangan memakan atau mengambil harta sesamanya dengan jalan yang tidak halal. Itu namanya memakan harta yang haram. Mengambil dan memakan harta orang lain dengan cara yang tidak halal itu banyak macamnya, misalnya dengan jalan mencuri, merampas, menipu, kemenangan judi, uang suap, jual beli barang yang terlarang dan riba. Salah satu jalan yang dihalalkan pengambilan dan pertukaran harta ialah perniagaan, jual beli yang dilakukan suka sama suka antara sipenjual dan si pembeli dengan cara jujur dan tidak ada penipuan di dalamnya. Termasuk mengambil dan memakan harta orang lain dengan cara yang batil, memajukan perkara ke depan pengadilan, supaya menjadi sah menurut hukum secara lahir, sedang pada hakikatnya adalah harta orang lain. Allah SWT berfirman: وَلا تَأْكُلُوا أَمْوَالَكُمْ بَيْنَكُمْ بِالْبَاطِلِ وَتُدْلُوا بِهَا إِلَى الْحُكَّامِ لِتَأْكُلُوا فَرِيقًا مِنْ أَمْوَالِ النَّاسِ بِالإثْمِ وَأَنْتُمْ تَعْلَمُونَ “Dan janganlah sebahagian kamu memakan harta sebahagian yang lain di antara kamu dengan jalan yang bathil dan (janganlah) kamu membawa (urusan) harta itu kepada hakim, supaya kamu dapat memakan sebahagian daripada harta benda orang lain itu dengan (jalan berbuat) dosa, Padahal kamu mengetahui.” (QS Al-Baqarah:188) Dapatlah dipahami bahwa putusan hakim (pengadilan) tidak dapat menjadikan yang haram itu menjadi halal menjadi haram pada sisi Tuhan, karena yang haram tetap haram dan yang halal tetap halal. Nabi saw. sesudah memberikan keputusan tentang suatu perkara harta benda, beliau pernah mengucapkan bahwa beliau memutuskannya menurut apa yang kelihatan menurut lahirnya, tetapi mungkin salah seorang di antara yang berperkara, yang satu lebih pintar lebih pandai berbicara dan lawannya, sehingga beliau memenangkan orang itu. Selanjutnya beliau memperingatkan, kalau putusan itu tidak tepat, berarti beliau memberikan kepada orang yang menang bara api. Kalau dia mau, silakan nengambi1nya sedikit atau banyak. Putusan Nabi sendiri tidak menghalalkan yang haram atau mengharamkan yang halal. Berkenaan dengan perniagaan sebagai suatu cara pemindahan dan peredaran harta yang dihalalkan, berdasarkan sukarela antara kedua belah pihak, si penjual dan si pembeli, masih ada beberapa hal yang perlu diperhatikan berkenaan dengan perniagaan ini. Ada perniagaan yang haram disebabkan oleh beberapa keadaan, misalnya menjual barang yang haram, barang terlarang memakan, meminum atau memakainya dan barang yang berasal dari curian dan rampasan. Seterusnya menjual barang yang tidak terang keadaannya, belum tentu baiknya atau tidak dapat dikirakan berapa jumlah yang sebenarnya. Terlarang pula mengurangi sukatan, ukuaran dan timbangan. Berkenaan dengan mengurangi sukatan, ukuran dan timbangan ini disebuutkan dalam firman Firman Allah SWT: وَأَوْفُوا الْكَيْلَ إِذَا كِلْتُمْ وَزِنُوا بِالْقِسْطَاسِ الْمُسْتَقِيمِ ذَلِكَ خَيْرٌ وَأَحْسَنُ تَأْوِيلا “Dan sempurnakanlah takaran apabila kamu menakar, dan timbanglah dengan neraca yang benar. Itulah yang lebih utama (bagimu) dan lebih baik akibatnya.” (QS. Al-Isra’:35) وَيْلٌ لِلْمُطَفِّفِينَ.الَّذِينَ إِذَا اكْتَالُوا عَلَى النَّاسِ يَسْتَوْفُونَ.وَإِذَا كَالُوهُمْ أَوْ وَزَنُوهُمْ يُخْسِرُونَ. “Kecelakaan besarlah bagi orang-orang yang curang, (yaitu) orang-orang yang apabila menerima takaran dari orang lain mereka minta dipenuhi, Dan apabila mereka menakar atau menimbang untuk orang lain, mereka mengurangi.” (QS. Al-Mutaffifin:1-3) Dalam melakukan perniagaan ini hendaklah ada kejujuran dan tidak ada penipuan. Dalam suatu hadis disebutkan, bahwa Rasulullah saw pada suatu waktu lewat di tempat orang menjual bahan makanan dan beliau tertarik melihatnya. Kemudian beliau memasukan tangannya dalam bahan makanan itu dan tangan Beliau kelihatan basah. Nabi bertanya kepada penjual bahan makanan, apa sebabnya begitu? Dijawab karena kena hujan. Nabi bersabda: “Mengapa tidak diletakkan sebelah atas supaya kelihatan. Kemudian beliau memberikan ancaman keras, dengan sabda beliau yang artinya: “Siapa yang menipu kita, dia bukan golongan kita”. (HR. Muslim). Kaurn saudagar apabila menjual barang yang ada cacatnya, hendaklah hal itu diterangkan dan siapa yang mengetahuinya wajib pula menerangkannya kepada si pembeli. Sabda Beliau yang artinya: “Seseorang menjual barang yang ada cacatnya, wajib menjelaskan cacat itu dan bagi orang yang mengetahuinvu, wajib pula menjelaskannya”.(Diriwayatkan oleh Hakim dan Baihaqi). Di samping perlindungan terhadap hak milik, diperlukan pula perlindungan terhadap nyawa. Sebab itu terlarang mumbunuh orang, apalagi membunuh diri sendiri, karena Allah itu sangat sayang kepada hambaNya. Membunuh itu adalah suatu kejahatan dan dosa besar, bisa menggemparkan dan mengganggu keamanan masyarakat. Sebab itu, dalam ayat lain disebutkan, bahwa siapa yang melanggar hak milik dan membunuh orang kepadanya diancam akan beroleh siksaan neraka di hari akhirat dan hukum kisas di dunia. Allah SWT berfirman: وَمَنْ يَفْعَلْ ذَلِكَ عُدْوَانًا وَظُلْمًا فَسَوْفَ نُصْلِيهِ نَارًا وَكَانَ ذَلِكَ عَلَى اللَّهِ يَسِيرًا ”Dan Barangsiapa berbuat demikian dengan melanggar hak dan aniaya, Maka Kami kelak akan memasukkannya ke dalam neraka. yang demikian itu adalah mudah bagi Allah.” (QS. An-Nisaa:30) Apabila perlindungan terhadap hak milik dan nyawa dapat berjalan dengan baik, tentu akan terciptalah keamanan dan ketenteraman dalam masyarakat. Sebaliknya dengan tidak ada perlindungan terhadap hak milik dan nyawa, akan terjadilah kekacauan dan silang sengketa yang tidak habis-habisnya.  Sumber disini

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Futur (Melemah atau Penurunan Kualitas Kegiatan Kebaikan), penyebab dan obatnya

Seorang penuntut ilmu tidak boleh futur dalam usahanya untuk memperoleh dan mengamalkan ilmu. Futur yaitu rasa malas, enggan, lamban dan tidak semangat, padahal sebelumnya ia rajin, bersungguh-sungguh dan penuh semangat.

Futur adalah satu penyakit yang sering menyerang sebagian ahli ibadah, para da'i dan penuntut ilmu. Sehingga menjadi lemah dan malas, bahkan terkadang berhenti sama sekali dari melakukan aktivitas kebaikan, misalnya futur dalam menuntut ilmu syar'i, futur dalam aktivitas dakwah, futur dalam beribadah kepada Allah dan lainnya.

Orang yang terkena penyakit futur ini ada 3 golongan:

1. Golongan yang berhenti sama sekali dari aktivitasnya dengan sebab futur, dan golongan ini banyak sekali.
2. Golongan yang terus dalam kemalasan dan patah semangat, namun tidak sampai berhenti sama sekali dari aktivitasnya, dan golongan ini lebih banyak lagi.
3. Golongan yang kembali pada keadaan semula, dan golongan ini sangat sedikit.

Futur memiliki banyak dan bermacam-macam sebab. Apabila seorang muslim  selamat dari sebagiannya, maka sedikit sekali kemungkinan selamat dari yang lainnya. Sebab-sebab ini sebagiannya ada  yang bersifat umum dan ada yang bersifat khusus.

Diantara sebab-sebab futur:

1. Hilangnya keikhlasan
2. Lemah dalam menuntut ilmu syar'i
3. Ketergantungan hati kepada dunia dan melupakan akhirat
4. Fitnah(cobaan) berupa istri, anak dan harta
5. Hidup di tengah masyarakat yang rusak.
6. Berteman dengan orang-orang yang memiliki keinginan yang lemah dan cita-cita duniawi
7. Melakukan dosa dan maksiat serta memakan barang-barang yang haram
8. Tidak mempunyai tujuan yang jelas (baik dalam menuntut ilmu maupun berdakwah)
9. Lemahnya iman
10. Menyendiri (tidak mau bergaul dengan komunitas yang baik)
11. Lemahnya pendidikan

Futur adalah penyakit yang sangat ganas, namun tidaklah Allah menurunkan penyakit melainkan Dia pun menurunkan obatnya. Akan mengetahui orang-orang yang mau mengetahuinya, dan tidak akan mengetahui orang-orang yang enggan mengetahuinya.

Diantara obat penyakit futur adalah:

1. Memperbaharui keimanan. Yaitu dengan mentauhidkan Allah dan memohon kepada-Nya agar ditambah keimanan, serta memperbanyak ibadah, menjaga shalat wajib yang lima waktu dengan berjamaah di masjid, mengerjakan shalat-shalat sunnah rawatib, melakukan shalat tahajjud dan witir. Begitu juga dengan bersedekah, silaturahmi, berbakti kepada kedua orang tua, dan lain-lain dari amal-amal ketaatan.
2. Merasa selalu diawasi Allah ta'ala dan banyak berdzikir kepada-Nya
3. Ikhlas dan bertakwa
4. Mensucikan hati (dari kotoran syirik, bid'ah dan kemaksiatan)
5. Menuntut ilmu, tekun menghadiri pelajaran, majelis taklim, muhadharah ilmiyyah dan dauroh-dauoroh syar'iyyah.
6. Mengatur waktu dan mengintrospeksi diri
7. Mencari teman yang baik (shalih)
8. Memperbanyak mengingat kematian dan takut terhadap su'ul khatimah (akhir kehidupan yang jelek)
9. Sabar dan belajar untuk sabar
10. Berdoa dan memohon pertolongan Allah

Sumber: Menuntut Ilmu, Jalan Menuju Sorga karya Yazid bin Abdul Qadir Jawas

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I’ll Stand By You

Oh, Why you look so sad?
Tears are in your eyes
Come on and come to me now
Don’t be ashamed to cry
Let me see you through
Cause I’ve seen the dark side too.
When the night falls on you
You don’t know what to do
Nothing you confess
could make me love you less

I’ll stand by you
I’ll stand by you
Won’t let nobody hurt you
I’ll stand by you

The Pretenders- I'll Stand by You (live) - More amazing video clips are a click away

So,
If your mad, get mad
Don’t hold it all inside
Come on and talk to me now
But hey, what you’ve got to hide
I get angry too
But I’m a lot like you
When you’re standing at the crossroads
Don’t know which path to choose
Let me come along
Cause even if your wrong…

I’ll stand by you
I’ll stand by you
Won’t let nobody hurt you
I’ll stand by you
Take me in into your darkest hour
And I’ll never desert you
I’ll stand by you
And when,
When the night falls on you baby
Your feeling all alone
Walking on your own

I’ll stand by you
I’ll stand by you
Won’t let nobody hurt you
I’ll stand by you
Take me in into your darkest hour
And I’ll never desert you
I’ll stand by you
I’ll stand by you
Won’t let nobody hurt you
I’ll stand by you
Won’t let nobody hurt you
I’ll stand by you
I’ll stand by you
Won’t let nobody hurt you
I`ll stand by you

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Mak Rempit di Malaysia

SEREMBAN, 11 Sept (Bernama) -- Mahkamah Majistret di sini pada Jumaat megenakan hukuman penjara 20 bulan dan denda RM8,000 terhadap seorang buruh setelah didapati bersalah terbabit dalam lumba motosikal haram di sini empat tahun lepas.

Majistret Mohd Aizuddin Zolkeply turut memerintahkan supaya lesen memandu tertuduh Jaini Jani, 26, dari Sikamat di sini digantung selama dua tahun mulai Jumaat.

Dalam penghakimannya, beliau berkata pihak pembelaan gagal menimbulkan keraguan munasabah.

Mengikut kertas pertuduhan, Jaini didakwa terbabit dalam lumba motosikal haram di Persiaran Senawang di sini di antara lampu isyarat stesen minyak Esso hingga lampu isyarat Taman Matahari Height pada 1.20 pagi, 12 Feb 2005.

Dia didakwa melakukan kesalahan itu mengikut Seksyen 42(1) Akta Pengangkutan Jalan (JPJ) 1987 yang membawa hukuman penjara tidak lebih lima tahun, denda tidak melebihi RM15,000 dan hilang kelayakan lesen memandu selama dua tahun.

Peguam tertuduh K. Indran dalam rayuannya berkata ini adalah kesalahan pertama tertuduh dan beliau mempunyai isteri dan anak.

Pegawai pendakwa C/Insp Jusman Ahmad pula berkata pada tahun lepas sebanyak 76 kali operasi lumba haram dijalankan manakala tahun ini sehingga bulan ini sebanyak 83 kali operasi yang sama diadakan.

"Di sini menunjukkan peningkatan operasi lumba haram di mana penunggang motosikal didapati tidak serik. Dengan itu, saya memohon pada mahkamah supaya tertuduh dihukum paling maksimum sebagai pengajaran. Lumba haram bukan saja membuang masa tapi merugikan diri sendiri," katanya.
sumber : harian bernama
diambil dari sini

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Etika Berdagang

1. Sikap jujur dalam berbicara
2. Berlaku sopan dan lembut kepada orang lain
3. Bangun pagi, berusaha mendapatkan sesuatu yang disyukuri
4. Selamat dari transaksi riba
5. Menunaikan zakat harta
6. Menolong yang lemah
7. Memuliakan tamu
8. Memelihara waktu shalat wajib
9. Ikhlas niatnya dalam ber-shadaqah

Merekalah orang -orang yang akan mendapat balasan dari Allah SWT, orang-orang berharta yang akan pergi dengan pahala. Orang-orang yang bekerja dengan baik, memiliki usaha yang disyukuri serta perdagangan yang tidak akan merugi. Mereka membangun masjid sebagai tempat ruku dan sujud, memberi makan kepada fakir miskin, memberi keringanan kepada mereka yang membutuhkan, serta menanggung hidup anak yatim. Mereka menghimpun kebaikan setiap waktu.

Orang pelit itu buruk sikapnya, sedangkan orang yang memberi akan banyak balasannya. Celakalah hamba uang , karena uang akan menunjukkan pemiliknya pada neraka, sebagaimana uang akan mengitari pemiliknya dengan keinginan.

Jika orang-orang justru menyimpan harta mereka di bank-bank, memelihara uang dalam dokumen-dokumen dan melindungi hartanya dengan pagar kawat maka janganlah kita seperti mereka. Jadilah orang yang menyimpan uang di bank Ar Rahmaan, peliharalah amalan kita dari syaitan, pagari niat dari keculasan dan kejahatan, ramaikan rumah dengan taqwa, berikan kemuliaan kepada tetangga, serta syukurilah apa yang telah diterima.

Penyakit para pedagang adalah kekurangan darah, keinginan berlebih, dan selalu gelisah. Kurang darah karena sibuk sehingga lupa makan, atau makannya tidak teratur. Banyak keinginan karena selalu disibukkan dengan uang, cek, serta simpanan di bank. Pikirannya tertuju pada urusan pengiriman dan penerimaan barang dagangannya. Kegelisahan muncul karena ambisinya selalu bertambah, selalu kuatir dengan nasib anak cucunya. Lalu kebahagiaan pergi darinya dan kesibukan menjadikannya tak sempat lagi beribadah.

Tak heran bahwa tema ilmu yang paling disenangi oleh pedagang yang kikir adalah tema yang menganjurkan hidup secara ekonomis. Adapun ilmu yang dibencinya adalah tema anjuran untuk banyak memberi dan ber-shadaqah.

Dr. Aidh bin Abdullah al Qarni, penulis Best Seller Laa Tahzan
Disadur dari Rubrik Wahat, Hal 68-69 Tarbawi Edisi 171 Th 8/Muharram 1429 H/17 Januari 2008 M
Judul asli: Tanamlah Uang di Bank Ar Rahmaan

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