function expand_nd,a
  s=(size(a,/dimensions))
  b=dblarr(s*2-1)*!values.d_nan
  for i=0,s[0]-1 do begin
    for j=0,s[1]-1 do begin
      for k=0,s[2]-1 do begin
        for l=0,s[3]-1 do begin
          b[i*2,j*2,k*2,l*2]=a[i,j,k,l]
        end
      end
    end
  end
  return,b
end