Laplace transform - MATLAB laplace (2024)

Laplace transform

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Syntax

F = laplace(f)

F = laplace(f,transVar)

F = laplace(f,var,transVar)

Description

example

F = laplace(f) returns the Laplace Transform of f. By default, the independent variable is t and the transformation variable is s.

example

F = laplace(f,transVar) uses the transformation variable transVar instead of s.

example

F = laplace(f,var,transVar) uses the independent variable var and the transformation variable transVar instead of t and s, respectively.

Examples

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Laplace Transform of Symbolic Expression

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Compute the Laplace transform of 1/sqrt(x). By default, the transform is in terms of s.

syms x yf = 1/sqrt(x);F = laplace(f)
F =

πs

Specify Independent Variable and Transformation Variable

Open Live Script

Compute the Laplace transform of exp(-a*t). By default, the independent variable is t, and the transformation variable is s.

syms a t yf = exp(-a*t);F = laplace(f)
F =

1a+s

Specify the transformation variable as y. If you specify only one variable, that variable is the transformation variable. The independent variable is still t.

F =

1a+y

Specify both the independent and transformation variables as a and y in the second and third arguments, respectively.

F = laplace(f,a,y)
F =

1t+y

Laplace Transforms of Dirac and Heaviside Functions

Open Live Script

Compute the Laplace transforms of the Dirac and Heaviside functions.

syms t ssyms a positiveF = laplace(dirac(t-a),t,s)
F =e-as
F = laplace(heaviside(t-a),t,s)
F =

e-ass

Relation Between Laplace Transform of Function and Its Derivative

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Show that the Laplace transform of the derivative of a function is expressed in terms of the Laplace transform of the function itself.

syms f(t) sDf = diff(f(t),t);F = laplace(Df,t,s)
F =slaplace(f(t),t,s)-f(0)

Laplace Transform of Array Inputs

Open Live Script

Find the Laplace transform of the matrix M. Specify the independent and transformation variables for each matrix entry by using matrices of the same size. When the arguments are nonscalars, laplace acts on them element-wise.

syms a b c d w x y zM = [exp(x) 1; sin(y) 1i*z];vars = [w x; y z];transVars = [a b; c d];F = laplace(M,vars,transVars)
F =

(exa1b1c2+1id2)

If laplace is called with both scalar and nonscalar arguments, then it expands the scalars to match the nonscalars by using scalar expansion. Nonscalar arguments must be the same size.

F = laplace(x,vars,transVars)
F =

(xa1b2xcxd)

Laplace Transform of Symbolic Function

Open Live Script

Compute the Laplace transform of symbolic functions. When the first argument contains symbolic functions, then the second argument must be a scalar.

syms f1(x) f2(x) a bf1(x) = exp(x);f2(x) = x;F = laplace([f1 f2],x,[a b])
F =

(1a-11b2)

If Laplace Transform Cannot Be Found

Open Live Script

If laplace cannot transform the input then it returns an unevaluated call.

syms f(t) sf(t) = 1/t;F(s) = laplace(f,t,s)
F(s) =

laplace(1t,t,s)

Return the original expression by using ilaplace.

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

1t

Input Arguments

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fInput
symbolic expression | symbolic function | symbolic vector | symbolic matrix

Input, specified as a symbolic expression, function, vector, or matrix.

varIndependent variable
t (default) | symbolic variable

Independent variable, specified as a symbolic variable. This variable is often called the "time variable" or the "space variable." If you do not specify the variable then, by default, laplace uses t. If f does not contain t, then laplace uses the function symvar to determine the independent variable.

transVarTransformation variable
s (default) | z | symbolic variable | symbolic expression | symbolic vector | symbolic matrix

Transformation variable, specified as a symbolic variable, expression, vector, or matrix. This variable is often called the "complex frequency variable." If you do not specify the variable then, by default, laplace uses s. If s is the independent variable of f, then laplace uses z.

More About

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Laplace Transform

The Laplace transform F(s) of the expression f(t) with respect to the variable t at the point s is a unilateral transform defined by

F(s)=0f(t)estdt.

Tips

  • If any argument is an array, then laplace acts element-wise on all elements of the array.

  • If the first argument contains a symbolic function, then the second argument must be a scalar.

  • To compute the inverse Laplace transform, use ilaplace.

Algorithms

The Laplace transform is defined as a unilateral or one-sided transform. This definition assumes that the signal f(t) is only defined for all real numbers t≥0, or f(t)=0 for t<0. Therefore, for a generalized signal with f(t)≠0 for t<0, the Laplace transform of f(t) gives the same result as if f(t) is multiplied by a Heaviside step function.

For example, both of these code blocks:

syms t;laplace(sin(t))

and

syms t;laplace(sin(t)*heaviside(t))

return 1/(s^2 + 1).

Version History

Introduced before R2006a

See Also

fourier | ifourier | ilaplace | iztrans | ztrans

Topics

  • Solve Differential Equations of RLC Circuit Using Laplace Transform

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Laplace transform - MATLAB laplace (1)

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Laplace transform - MATLAB laplace (2024)
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