// save img as PGM(P2,ascii) image format
function imshow(img)
  w=size(img,2);
  h=size(img,1);
  
  fd=mopen('save.pgm', 'w');
  mfprintf(fd, 'P2\n%d %d\n255\n', w, h);
  
  for i=1:h
    for j=1:w
      mfprintf(fd,'%d ', img(i,j)*255); 
    end
  end
  
  mclose(fd);
  
endfunction