Creating 4D vector inside parfor

This is what I have

parfor i = 1:N/k 
    tti=-sqrt(N)/2+(i*k-k)/sqrt(N);
    [ap,~]=meshgrid(tau/2+tti,tau/2);
    [am,~]=meshgrid(tau/2-tti,tau/2);
    for j = 1: N/k 
        ttj=-sqrt(N)/2+(j*k-k)/sqrt(N);
        [~, b]=meshgrid(tau/2+tti,tau/2+ttj);
        m1 = interp2(t,t,x,ap,b);
        [~, b]=meshgrid(tau/2-tti,tau/2-ttj);
        m2 = conj(interp2(t,t,x,am,b));
        mm=real(fftshift(fft2(ifftshift( m1.*m2  ))));
        W(i,j,:,:)=mm(1 : k: N,1 : k: N);
    end
end

It doesn't like the way I index W, but clearly different loops do not try to overwrite each other.

The variable W in a parfor cannot be classified

How can I fix it?

I tried this:

parfor

   i = 1:N/k %actually 1:4:N
      tti=-sqrt(N)/2+(i*k-k)/sqrt(N);
      [ap,~]=meshgrid(tau/2+tti,tau/2);
      [am,~]=meshgrid(tau/2-tti,tau/2);
      WW=zeros(N/k,N/k,N/k);
      for j = 1: N/k %actually 1:4:N
          ttj=-sqrt(N)/2+(j*k-k)/sqrt(N);
          [~, b]=meshgrid(tau/2+tti,tau/2+ttj);
          m1 = interp2(t,t,x,ap,b);
          [~, b]=meshgrid(tau/2-tti,tau/2-ttj);
          m2 = conj(interp2(t,t,x,am,b));
          mm=real(fftshift(fft2(ifftshift( m1.*m2  ))));
          WW(j,:,:)=mm(1 : k: N,1 : k: N);
      end
      W(i,:,:,:)=WW;
  end

and it worked, but is it working as I want it to?

Answer 1

[Walter Roberson]

The approach you use in your second code is correct.