Adding constraints to function plots in 2-D and 3-D

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Adekunle Rotimi Adekoya 2021-8-27

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https://ww2.mathworks.cn/matlabcentral/answers/1441939-adding-constraints-to-function-plots-in-2-d-and-3-d

回答： Wan Ji 2021-8-29

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Hi,

I am new to Matlab.

I have the code snippet below.

Assume that I want to skip parts of the domain of f, i.e. (x,y), where x^2 + y^2 = c (c is any constant value in my code).

So, I want the mesh function to only plot functional values of the points in the domain of my function, which satisfify the above constraint.

How do I go about editing the code snippet below in order to incorporate the type of constraint defined above?

You timely assistance would be appreciated.

f = @ (x , y ) x .* sin( x .* y );

[X , Y ] = meshgrid (0:.1:5 , pi :.01* pi :2* pi );

Z = f (X , Y );

mesh (X ,Y , Z )

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Wan Ji 2021-8-27

I feel a litlle bit confused of your question, which domain should be skipped?

x^2+y^2<c

or

x^2+y^2>c

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Answer 1

Wan Ji 2021-8-29

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https://ww2.mathworks.cn/matlabcentral/answers/1441939-adding-constraints-to-function-plots-in-2-d-and-3-d#answer_776449

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Hi,

I have translated the Cartesian to polar system so as to satisfy your requirement

f = @ (x , y ) x .* sin( x .* y );
minR = sqrt(0+pi^2);
maxR = sqrt(5^2+(2*pi)^2);
minTheta = atan2(pi,5);
maxTheta = atan2(2*pi,0);
r = linspace(minR, maxR, 101);
theta = linspace(minTheta, maxTheta, 101);
[R, T] = meshgrid(r, theta);
X = R.*cos(T);
Y = R.*sin(T);
% [X , Y ] = meshgrid (0:.1:5 , pi :.01* pi :2* pi );
Z = f (X , Y );
Z(~(X<=5 & X>=0 & Y<=2*pi & Y>=pi)) = NaN;
mesh (X ,Y , Z )