Subscript indices must either be real positive integers or logicals. How to solve it?

Hi, I know this is asked very often, but still I don't know how to solve it in my case. This is the code:

M=4;

n = zeros(1,M);

q=[0:M-1]*(2/M);

for i1=1:M

      for i2=1:M

          n(q)=n(q)+exp(-1i*q*(i1-i2))*A(i1,i2);

      end

end

I received this error message: "Subscript indices must either be real positive integers or logicals.""

Could you please help me?

Cheers!

[Stephen23]

These are the values that you are using for indexing:

>> q=[0:M-1]*(2/M)
q =
   0.00000   0.50000   1.00000   1.50000

Do they look like real positive integers to you?

[Auryn_]

I know there are not, but those are the values needed.

[Geoff Hayes]

Auryn_ - what should the integer equivalents of these be? I don't think that you can just round each up to the nearest positive integer because then you will have two that are identical (0 and 0.5). What is the reasoning behind your choice of q?

[Auryn_]

Hi Geoff,

The q/{\pi} values are the points in momentum space, which are between [0,2\pi).

[Rik]

This sounds like you want to interpolate/resample your data. You can find dozens of examples using your favorite internet search engine.

[Lorenzo Meneghetti]

when you do n(q) q is zero so it gives error

arrays in matlab are accessed with indices starting from 1

also you didn't define A

[Auryn_]

Yes, it's like the Fourier transform directly. I need the points between [0,2\pi).