Laplace Transform MATLAB

Introduction to Laplace Transform MATLAB

MATLAB is a programming environment that is interactive and is used in scientific computing. It is extensively used in a lot of technical fields where problem-solving, data analysis, algorithm development, and experimentation is required. The software which is discipline-specific is extensively written using MATLAB.

In this article, we will study the MATLAB function used to calculate the Laplace transform. Before we get into details of how Laplace function works in MATLAB, let us refresh our understanding of Laplace transform.

Laplace transformation is used to solve differential equations. In Laplace transformation, the differential equation in the time domain is first converted or transformed into an algebraic equation in the frequency domain. Next, this algebraic equation is solved and the result is transformed into the time domain. This will be our solution of the differential equation. In simpler words, Laplace transformation is a quick method to solve differential equations.

Syntax

Let us understand the Syntax of Laplace function in MATLAB

Laplace (f)

Description of Laplace function in MATLAB:

• laplace (f) returns the Laplace transform of the input ‘f’.

Examples to Implement Laplace Transform MATLAB

Let us now understand Laplace function with the help of a few examples

Example #1

In the first example, we will compute laplace transform of a sine function using laplace (f): Lets us take asine signal defined as:

• 4 * sin (5 * t)

Mathematically, the output of this signal using laplace transform will be:

• 20/ (s^2 + 25), considering that transform is taken with ‘s’ as transformation variable and ‘t’ as independent variable.

Syntax

syms t[Initializing the variable] f = 4*sin(5*t);[Input sine function] Lt = laplace(f)[Using the laplace function to get the laplace transform]

Code:

syms t
f = 4*sin (5*t);
Lt = laplace (f)

Output:

As we can see, the transform is in terms of the variable ‘s’ and the output is as expected by us.

Example #2

Here is an example where we compute laplace transform of a cosine signal using laplace (f):

Lets us take cosine signal defined as:

• cos (t) + cos (3 *t) ;

Mathematically, our output should be:

• s / (s ^ 2 + 1) + s / (s ^ 2 + 9)

Syntax

syms t[Initializing the variable] f = cos (t) + cos (3 *t) ;[Input cos function] Lt = laplace(f)[Using the laplace function to get the laplace transform]

Code:

syms t
f = cos (t) + cos (3 * t) ;
Lt = laplace (f)

Output:

As we can see, the Laplace transform is calculated w.r.t ‘s’ and the output is as expected by us.

Example #3

In the next example we will compute Laplace transform of an exponential function using laplace (f):

Lets us take an exponential function defined as:

• exp (-2*a^2);

Mathematically, our output should be:

• (2^ (1/2) *pi^ (1/2) *exp (s^2/8) *erfc( (2^ (1/2) *s) /4) ) /4

Syntax

syms a[Initializing the variable] f = exp (-2 *a^2) ;[Input exponential function] Lt  = laplace(f)[Using the laplace function to get the laplace transform]

Code:

syms a
f = exp (-2 *a^2);
Lt  = laplace (f)

Output:

As we can see, the laplace transform is calculated w.r.t ‘s’ and the output is as expected by us.

Example #4

Next, we will learn to calculate Laplace transform of a matrix. In the case of a matrix,the function will calculate laplace transform of individual elements of the matrix.

Below is the example where we calculate Laplace transform of a 2 X 2 matrix using laplace (f): Lets us define our matrix as:

• Z = [exp (2x) 1; sin (y) cos (z) ];

Now for each element in the matrix, we need to pass transformation & independent variables.

• Let us define our independent variables as:Variables = [w a; b c];
• And Transform variables as:Transfrom_Variables = [p q; r s];

Mathematically, our output should be:

• [ exp (2x) /p,     1/q] [ sin (y) /r, cos (z) /s]

Syntax

syms a b c w p q r s[Initializing the variables] Z = [exp (2x)     1;   sin (y)    cos (z)];[Input matrix with different signals] Variables = [w a; b c];[Independent variables] Transfrom_Variables = [p q; r s];[Transformation variables] laplace(Z,Variables,Transfrom_Variables)

Code:

syms a b c d w x y z
Z = [exp (2*x) 1; sin (y) cos (z)];
Variables = [w a; b c];
Transfrom_Variables = [p q; r s];
laplace (Z, Variables, Transfrom_Variables)

Output:

As we can see, we have got the laplace transform of every element in the matrix Z.

Conclusion

Laplace function is used in MATLAB to calculate the laplace transform of a function. We can calculate the Laplace transform w.r.t to the default transformation variable‘s’or the variable we define as the transformation variable.

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