How to plot a convergence graph for a double sum?

2021 11 10
1 个回答
更新时间：2021 11 11
5 次查看（30 天）

0 个投票

I'm trying to show converengence for a double sum but I can't figure out how to plot the convergence. I think I need to create an array to store the previous values of the series but I'm not sure how to do that.
This is the series I'm trying to graph:
This is my current code:
T=0; %terms used in series
q_m=0;
M=15000;
N=15000;
x=2.5;
y=3.5;
for n=1:N
for m=1:M
T=T+1;
q_m1 = (400/(m*n*pi^2))*(cos(n*pi*4/10)-cos(n*pi*3/10))*(cos(m*pi*3/10)-cos(m*pi*2/10))*sin(m*pi*x/10)*sin(n*pi*y/10);
q_m = q_m + q_m1;
end
end
q_m
T

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回答（1 个）

VBBV
VBBV 2021-11-10
编辑：VBBV 2021-11-11
Ran in:

1 个投票

Ran in:
T=0; %terms used in series
M=15;
N=15;
q_m=zeros(M,1);
qq_m=zeros(M,1);
x=2.5;
y=3.5;
for n=1:N
for m=1:M
T=T+1;
q_m1 = (400/(m*n*pi^2))*(cos(n*pi*4/10)-cos(n*pi*3/10))*(cos(m*pi*3/10)-cos(m*pi*2/10))*sin(m*pi*x/10)*sin(n*pi*y/10);
q_m(m) = q_m1;
end;
qq_m(n) = sum(q_m);
end
plot(qq_m)
T
T = 225
You can modify the code as above to plot convergence

4 个评论
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VBBV
VBBV 2021-11-10
Read also about symsum function to know more.
Elizabeth McLean
Elizabeth McLean 2021-11-11
Thank you so much! This is just what I needed. I wasn't making the conection of using the index to fill in rows of a matrix.
Star Strider
Star Strider 2021-11-11
@Elizabeth McLean — It is appropriate and appreciated to Accept answers that solve the problem.
Elizabeth McLean
Elizabeth McLean 2021-11-11
Sorry about that, this is my first time asking a question. I've accepted the answer now.

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VBBV
VBBV
2021-11-11

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