Laplace transform
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Syntax
F = laplace(f)
F = laplace(f,transVar)
F = laplace(f,var,transVar)
Description
example
returns the Laplace Transform of F
= laplace(f)f
. By default, the independent variable is t
and the transformation variable is s
.
example
uses the transformation variable F
= laplace(f,transVar)transVar
instead of s
.
example
uses the independent variable F
= laplace(f,var,transVar)var
and the transformation variable transVar
instead of t
and s
, respectively.
Examples
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Laplace Transform of Symbolic Expression
Open Live Script
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 =
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 =
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 = laplace(f,y)
F =
Specify both the independent and transformation variables as a
and y
in the second and third arguments, respectively.
F = laplace(f,a,y)
F =
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 =
F = laplace(heaviside(t-a),t,s)
F =
Relation Between Laplace Transform of Function and Its Derivative
Open Live Script
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 =
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 =
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 =
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 =
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) =
Return the original expression by using ilaplace
.
f(t) = ilaplace(F,s,t)
f(t) =
Input Arguments
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f
— Input
symbolic expression | symbolic function | symbolic vector | symbolic matrix
Input, specified as a symbolic expression, function, vector, or matrix.
var
— Independent 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.
transVar
— Transformation 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
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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