Dear Community!

I'm struggleing with a problem long since. I highly appreciate any help with this theme.

The problem is the following:

- I have a set of points, what comes from a numerical solution of a complex, but periodical function. Therefore I have a set of points (X;Y). The points are doesn't matter, but in my case, it look like this:

I want to use the Fourier-method to approximate this points with a function.

The best result I could get is this:

But it is not acceptable due to the high inaccuracy at the starting, and finishing points (there is a diagram inaccuracy %):

I'm feel like, I'm doing something wrong. Unfortunately, I had no time to look deep into the math here. Can somebody tell me, that how can I get a better result, using this method?

Thank you very much for the help in advance.

Best regards

Dávid

Hello dear users!

I have a problem, that I can not explain, and solve by myself. I have a function. It is an integral function, looks like this:

If I looking for a value such as LL(4) or LL(5) I got different value what i except from the plot of the function:

while, for example: evalf( LL(3))=1.6829

Can somebody explain to me, what is going on?

Also, if i want to solve the functiuon backwards with fsolve (so im looking for the phi values with the added LL(phi) value, sometimes I got results and sometimes not. (and not where the distruption is, because I know there the values go from -infinity to infinity). Can somebody help me in this too?

Thank you very much!