List of Laplace transforms

The following is a list of Laplace transforms for many common functions of a single variable.[1] The Laplace transform is an integral transform that takes a function of a positive real variable t (often time) to a function of a complex variable s (complex angular frequency).

Properties

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The Laplace transform of a function can be obtained using the formal definition of the Laplace transform. However, some properties of the Laplace transform can be used to obtain the Laplace transform of some functions more easily.

Linearity

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For functions and and for scalar , the Laplace transform satisfies

and is, therefore, regarded as a linear operator.

Time shifting

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The Laplace transform of is .

Frequency shifting

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is the Laplace transform of .

Explanatory notes

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The unilateral Laplace transform takes as input a function whose time domain is the non-negative reals, which is why all of the time domain functions in the table below are multiples of the Heaviside step function, u(t).

The entries of the table that involve a time delay τ are required to be causal (meaning that τ > 0). A causal system is a system where the impulse response h(t) is zero for all time t prior to t = 0. In general, the region of convergence for causal systems is not the same as that of anticausal systems.

The following functions and variables are used in the table below:

Table

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Function Time domain
Laplace s-domain
Region of convergence Reference
unit impulse all s inspection
delayed impulse Re(s) > 0 time shift of
unit impulse[2]
unit step Re(s) > 0 integrate unit impulse
delayed unit step Re(s) > 0 time shift of
unit step[3]
ramp Re(s) > 0 integrate unit
impulse twice
nth power
(for integer n)
Re(s) > 0
(n > −1)
Integrate unit
step n times
qth power
(for complex q)
Re(s) > 0
Re(q) > −1
[4][5]
nth root Re(s) > 0 Set q = 1/n above.
nth power with frequency shift Re(s) > −α Integrate unit step,
apply frequency shift
delayed nth power
with frequency shift
Re(s) > −α Integrate unit step,
apply frequency shift,
apply time shift
exponential decay Re(s) > −α Frequency shift of
unit step
two-sided exponential decay
(only for bilateral transform)
α < Re(s) < α Frequency shift of
unit step
exponential approach Re(s) > 0 Unit step minus
exponential decay
sine Re(s) > 0 [6]
cosine Re(s) > 0 [6]
hyperbolic sine Re(s) > |α| [7]
hyperbolic cosine Re(s) > |α| [7]
exponentially decaying
sine wave
Re(s) > −α [6]
exponentially decaying
cosine wave
Re(s) > −α [6]
natural logarithm Re(s) > 0 [7]
Bessel function
of the first kind,
of order n
Re(s) > 0
(n > −1)
[7]
Error function Re(s) > 0 [7]

See also

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References

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  1. ^ Distefano, J. J.; Stubberud, A. R.; Williams, I. J. (1995), Feedback systems and control, Schaum's outlines (2nd ed.), McGraw-Hill, p. 78, ISBN 978-0-07-017052-0
  2. ^ Riley, K. F.; Hobson, M. P.; Bence, S. J. (2010), Mathematical methods for physics and engineering (3rd ed.), Cambridge University Press, p. 455, ISBN 978-0-521-86153-3
  3. ^ Lipschutz, S.; Spiegel, M. R.; Liu, J. (2009), "Chapter 33: Laplace transforms", Mathematical Handbook of Formulas and Tables, Schaum's Outline Series (3rd ed.), McGraw-Hill, p. 192, ISBN 978-0-07-154855-7
  4. ^ Lipschutz, S.; Spiegel, M. R.; Liu, J. (2009), "Chapter 33: Laplace transforms", Mathematical Handbook of Formulas and Tables, Schaum's Outline Series (3rd ed.), McGraw-Hill, p. 183, ISBN 978-0-07-154855-7
  5. ^ "Laplace Transform". Wolfram MathWorld. Retrieved 30 April 2016.
  6. ^ a b c d Bracewell, Ronald N. (1978), The Fourier Transform and its Applications (2nd ed.), McGraw-Hill Kogakusha, p. 227, ISBN 978-0-07-007013-4
  7. ^ a b c d e Williams, J. (1973), Laplace Transforms, Problem Solvers, George Allen & Unwin, p. 88, ISBN 978-0-04-512021-5