title: OpenCV matrix multiplication assertion
body: <p>I'm getting</p>
  
  <pre><code>OpenCV Error: Assertion failed (type == B.type() &amp;&amp; (type == CV_32FC1 || type == CV_64FC1 || type == CV_32FC2 || type == CV_64FC2)) in gemm, file /build/buildd
  /opencv-2.4.9+dfsg/modules/core/src/matmul.cpp, line 711
  terminate called after throwing an instance of 'cv::Exception'
    what():  /build/buildd/opencv-2.4.9+dfsg/modules/core/src/matmul.cpp:711: error: (-215) type == B.type() &amp;&amp; (type == CV_32FC1 || type == CV_64FC1 || type == 
  CV_32FC2 || type == CV_64FC2) in function gemm
  </code></pre>
  
  <p>I'd like to know where in the docs it's mentioned matrix multiplication is supported solely for floating point matrices? I could only find people telling this in SO, but nothing so far comparable to a standard documentation.</p>