# Fourier expansion of dirac delta function

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Emre Gemici on 6 Apr 2022
Commented: Emre Gemici on 7 Apr 2022
Hi,
I am working on moving loads on beams and load is defiend by delta function as:
Sum of the series at x=v0*t must be equal to F0 for every n values. Below is my code that plots F0 and with increasing n value it also increases. I can't find what is wron with my code or isomething is wrong with the formulation?
L=10;
F0=10000;
v0=1;
t=4;
x=-10:0.1:10;
n=4;
f=0;
for i=1:n
wn=i*pi/L;
f=f+2*F0/L*sin(wn*v0*t)*sin(wn*x);
end
plot(x, f);
grid;
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### Accepted Answer

Paul on 6 Apr 2022
Increasing n to better approximate the infinte sum yields
L=10;
F0=10000;
v0=1;
t=4;
x=-10:0.1:10;
n=400;
f=0;
for i=1:n
wn=i*pi/L;
f=f+2*F0/L*sin(wn*v0*t)*sin(wn*x);
end
plot(x, f);
grid;
Don't know if that's what's expected.
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Emre Gemici on 7 Apr 2022
Ahh of course. F0 is not equal to peak value of the curve, it is equal to area under the curve between 0 and L. There is no need to restrict x or y. It is a periodic function with period of 2L (-L to L) but since our interval is 0 to L it is multiplied by 2. Thanks for helping.

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