Plot double Fourier series in MATLAB

Question

Amin Ghasemi 2016-11-10

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/311627-plot-double-fourier-series-in-matlab

回答： Amin Ghasemi 2016-11-11

采纳的回答： Amin Ghasemi

在 MATLAB Online 中打开

I'd like to plot 'mesh' for both f and g functions in MATLAB.

I'd tried this for f and g:

clc
clear
close all
%%plot f
[x,y] = meshgrid(linspace(-pi,pi,50));
f=x.*y ;
subplot(1,2,1)
mesh(f)
title('f')
%%plot g
A=4*(-1)^(m+n)*(sin(m.*x)*sin(n.*y))/(m*n);
g=sum(sum(A,n,1,inf),m,1,inf);
subplot(1,2,2)
mesh(g)
title('g')

The result is:

I don't have any idea to plot g directly from its' function, any help would be appreciated.

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Amin Ghasemi 2016-11-11

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/311627-plot-double-fourier-series-in-matlab#answer_242880

在 MATLAB Online 中打开

finally I found the solution, thanks all.

clc
clear
close all
%%plot f
[x,y] = meshgrid(linspace(-pi,pi,40));
f=x.*y ;
subplot(1,2,1)
mesh(f)
title('f(x,y)=xy')
%%plot g
syms m n X Y
assume(m>=1);
assume(n>=1);
assume(X>-pi & X<pi);
assume(Y>-pi & Y<pi);
A = 4*(-1)^(m+n)*(sin(m*X)*sin(n*Y))/(m*n);
g = real(double(subs(symsum(symsum(A,n,1,Inf),m,1,Inf),{X,Y},{x,y})));
subplot(1,2,2)
mesh(g)
title('g: Double Fourier series of  f  for  -\pi  to  \pi ')

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

Answer 2

Daniel kiracofe 2016-11-11

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/311627-plot-double-fourier-series-in-matlab#answer_242859

I think your problem is this line

A=4*(-1)^(m+n)*(sin(m.*x)*sin(n.*y))/(m*n);

from the way you have written it, it looks like you are expecting matlab to treat 'm' and 'n' as symbols here, for later evaluation in the sum command. But by default, matlab does not do symbolic computation. it does numeric computation. it is expecting m and n to be numbers (or vectors, or matrices). I think what you wanted to do was to first declare m and n to be symbols (i.e "syms n m"), and then use symsum() instead of sum(). Look up the documentation for the symbolic math toolbox for more information.