an class="string">'!'</span>); <span class="keyword">end</span>
0019 <span class="keyword">if</span> nargin&lt;3 || isempty(shifts); shifts=[0]; <span class="keyword">end</span>
0020 
0021 <span class="keyword">if</span> isnumeric(x)
0022     <span class="comment">% x and y are matrices</span>
0023     <span class="keyword">if</span> size(y,1)~=size(x,1); error(<span class="string">'!'</span>); <span class="keyword">end</span>
0024     <span class="keyword">if</span> size(y,3)~=size(x,3); error(<span class=