title: zero padding in fft
body: <p>Let <code>h</code> be a 5x5 matrix, why does zero-padding using <code>fft2</code> as in </p>
  
  <pre><code>H = fft2(h,250,250);
  </code></pre>
  
  <p>not give the same result as using <code>padarray</code> manually, as in</p>
  
  <pre><code>H = fft2(padarray(H,[122 122]));
  </code></pre>
  
  <p>Is it because in my second example, the padded matrix is only 249 columns and rows? Should I add an extra column/row of zeros?</p>