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ilaplace

Inverse Laplace transform

Syntax

ilaplace(F,trans_var,eval_point)

Description

ilaplace(F,trans_var,eval_point) computes the inverse Laplace transform of F with respect to the transformation variable trans_var at the point eval_point.

Input Arguments

F

Symbolic expression or function, vector or matrix of symbolic expressions or functions.

trans_var

Symbolic variable representing the transformation variable. This variable is often called the "complex frequency variable".

Default: The variable s. If F does not contain s, then the default variable is determined by symvar.

eval_point

Symbolic variable or expression representing the evaluation point. This variable is often called the "time variable".

Default: The variable t. If t is the transformation variable of F, then the default evaluation point is the variable x.

Examples

Compute the inverse Laplace transform of this expression with respect to the variable y at the evaluation point x:

syms x y
F = 1/y^2;
ilaplace(F, y, x)
ans =
x
 

Compute the inverse Laplace transform of this expression calling the ilaplace function with one argument. If you do not specify the transformation variable, ilaplace uses the variable s:

syms a s x
F = 1/(s - a)^2;
ilaplace(F, x)
ans =
x*exp(a*x)

If you also do not specify the evaluation point, ilaplace uses the variable t:

ilaplace(F)
ans =
t*exp(a*t)
 

Compute the following inverse Laplace transforms that involve the Dirac and Heaviside functions:

syms s t
ilaplace(1, s, t)
ans =
dirac(t)
ilaplace(exp(-2*s)/(s^2 + 1) + s/(s^3 + 1), s, t)
ans =
heaviside(t - 2)*sin(t - 2) - exp(-t)/3 +...
(exp(t/2)*(cos((3^(1/2)*t)/2) + 3^(1/2)*sin((3^(1/2)*t)/2)))/3
 

If ilaplace cannot find an explicit representation of the transform, it returns an unevaluated call:

syms F(s) t
f = ilaplace(F, s, t)
f(t) =
ilaplace(F(s), s, t)

laplace returns the original expression:

laplace(f, t, s)
ans(s) =
F(s)

More About

expand all

Inverse Laplace Transform

The inverse Laplace transform is defined by a contour integral in the complex plane:

Here c is a suitable complex number.

Tips

  • If you call ilaplace with two arguments, it assumes that the second argument is the evaluation point eval_point.

  • If F is a matrix, ilaplace applies the inverse Laplace transform to all components of the matrix.

  • To compute the direct Laplace transform, use laplace.

See Also

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