I am getting NaN values after some iterations in my loop

I get NaN values after few iterations using fourier transform this happens every time I add the fourier transform of V*psi into the equation for that I am using fft fxn

X=(-M/2:M/2-1)*dx;
dk=2*pi/(M*dx);
K=(-M/2:M/2-1)*dk;
 psi=(1/sqrt(2)).*randn(1,M)+(i/sqrt(2)).*randn(1,M);
  V=(X.^2)/2;
 Tmax=40;
dt=0.004;
Nt=round(Tmax/dt);
Fpsi=zeros(Nt+1,M);
 FVpsi=zeros(Nt,M);
  Fpsisq=zeros(Nt,M);
 for t=1:Nt
      Fpsi(t,:)=fft(psi(t,:));
      FVpsi(t,:)=fft(V.*psi(t,:));
      Fpsisq(t,:)=fft((abs(psi(t,:)).^2).*psi(t,:));
    Fpsi(t+1,:)=Fpsi(t,:)+dt.*(K.*K.*Fpsi(t,:)+FVpsi+g.*Fpsi);
     psi(t+1,:)=ifft(Fpsi(t+1,:));
 end

Answer 1

[Matt J]

To find out where they are first introduced, you can use,

>> dbstop if naninf

[Lovelesh Lovelesh]

But it do not give the right results then because iterations becomes very less

[Matt J]

It's supposed to stop before finishing.