MATLAB: How can i find a variable that is in the infinite series

infinite seriesseries

Hello everyone,
I'm trying to learn MATLAB on my own, and I have a problem. I got this equation and i know everything except 'L' in the infinite series. I need to find it, but i couldn't solve it when it is in the infinite series.
Deff=(2.02)*10^(-10);
t=22320;
a=0.1425; % a is equal to ((X-X*)/(X0-X*))*(pi^2)/8
n=1:10000;
Ser = @(L) sum((exp(((pi^2)*(-1)*Deff*t*(2*n-1))./(4*L.^2))/((2*n-1).^2)));
L = fzero(@(L) Ser(L)-a,0)
I wrote this but i couldn't find L. Could someone help me please??

Best Answer

Deff=(2.02)*10^(-10);
t=22320;
a=0.1425;
n=1:100000;
Ser = @(L) sum(1./(2*n-1).^2.*exp(-(2*n-1).^2*pi^2*Deff*t/4/L^2));
l= fzero(@(L) Ser(L)-a,.0024);
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