ft.m

function z = ft(a,dims)
   
% function z = ft(a,[dims]);
% fft of a with zero frequency in center
% if dims is given, perform fft on dimension(s) given
% else perform fft on all dimensions

if nargin==1
    z = fftshift(fftn(fftshift(a)));
else
    z = a;
    for d=1:length(dims)
        dim = dims(d);
        z = fftshift(fft(fftshift(z,dim),[],dim),dim);
    end
end