how to do a contour plot using function handle?

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U B
U B 2024-7-22
评论： Star Strider 2024-7-23
Ran in:
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.
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U B
U B 2024-7-22
I'm using 2021a. But providing arguments to M, as suggested by another answer works. Thank you.
Aquatris
Aquatris 2024-7-22
I tried in 2019b, and just giving function to the fcontour function also works. No need to provide arguments to the M. Interesting behaviour.

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Star Strider
Star Strider 2024-7-22
Ran in:
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))
.
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更多回答（1 个）

Muskan
Muskan 2024-7-22
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":
  1. Define the function handle to take two separate inputs.
  2. 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
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Stephen23
Stephen23 2024-7-22
编辑：Stephen23 2024-7-22
"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)
source: https://www.mathworks.com/help/matlab/ref/fcontour.html#bu62qy6-1-f
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.
Muskan
Muskan 2024-7-22
编辑：Muskan 2024-7-22
Hi, I likely missed catching that, thank you for pointing that out, that helps a lot!

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