# how to do a contour plot using function handle?

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By creating meshgrid, I can do contour plot.

T=linspace(0,2*pi,100);

d = linspace(0,2*pi,100) ;

[X,Y] = meshgrid(T,d);

M =(sin(Y).*sin(2.*X)) ;

contourf(X*(180/pi),Y*(180/pi),M)

But when I try to do it as

M = @(T,d)(sin(d).*sin(2.*T)) ;

fcontour(M)

I'm not able to get any graph. If anybody can explain to me how this works. Appriciate your help.

##### 3 Comments

Aquatris
on 22 Jul 2024

### Accepted Answer

Star Strider
on 22 Jul 2024

Provide arguments to ‘M’ and it works —

T=linspace(0,2*pi,100);

d = linspace(0,2*pi,100) ;

[X,Y] = meshgrid(T,d);

M = @(T,d)(sin(d).*sin(2.*T)) ;

figure

contourf(M(X,Y))

.

##### 4 Comments

### More Answers (1)

Muskan
on 22 Jul 2024

Hi,

As per my understanding the issue occurs because because "fcontour" needs a function handle that takes two individual scalar inputs, not a single vector. So, the correct approach is to define the function handle in such a way that it matches fcontour's expected input.

You can follow the following steps to properly define and use the function handle with "fcontour":

- Define the function handle to take two separate inputs.
- Use "fcontour" with the correct function handle and specify the range for "T" and "d".

Here is a code snippet on how you can achieve the same:

% Define the function handle to take two separate inputs

M = @(T, d) sin(d).*sin(2.*T);

% Plot using fcontour

fcontour(M, [0 2*pi 0 2*pi])

xlabel('T (radians)')

ylabel('d (radians)')

title('Contour plot of sin(d) * sin(2*T)')

Kindly refer to the following documentation of "fcontour" for more information: https://www.mathworks.com/help/matlab/ref/fcontour.html

##### 2 Comments

Stephen23
on 22 Jul 2024

Edited: Stephen23
on 22 Jul 2024

"As per my understanding the issue occurs because because "fcontour" needs a function handle that takes two individual scalar inputs, not a single vector. "

The FCONTOUR documentation actually states that "The function must accept two matrix input arguments and return a matrix output argument of the same size." (bold added)

The OP's code does not accept "a single vector", it accepts two matrices.

"So, the correct approach is to define the function handle in such a way that it matches fcontour's expected input."

It already does.

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