How to fill a matrix with a condition?

Question

Juraj 2013-12-8

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评论： sixwwwwww 2013-12-8

Hello,

I want to make some plots, and for that I need a matrix of which every element corresponds to one point in the xy plane, so I have:

[x,y]=meshgrid(-35:.25:35);
[phi,rho]=cart2pol(x,y);

The way I normally do it is:

z(:,:)=<some function I want to plot which includes rho and phi>

This time I need a condition: for rho<=25 I want different function values than for 25<rho&&rho<35. How can this be done? I tried to use a loop:

if rho<=25
   z(:,:)=<some function values>
else 
   z(:,:)=<some other values>

but that didn't work.

Thanks for the help.

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Answer 1

sixwwwwww 2013-12-8

1
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/109070-how-to-fill-a-matrix-with-a-condition#answer_117714

编辑：sixwwwwww 2013-12-8

在 MATLAB Online 中打开

try doing it like this:

[x, y] = meshgrid(-35:.25:35);
[phi, rho] = cart2pol(x, y);
z = zeros(size(x));
z(rho <= 25) = rho(rho <= 25) - phi(rho <= 25); % Here you can use your function 1
z(rho > 25) = rho(rho > 25) + phi(rho > 25); % Here you can use your function 2
mesh(x, y, z)

I hope it helps. Good luck!