n the first variant of this method, the train descriptors are passed as an input argument. In the
     second variant of the method, train descriptors collection that was set by DescriptorMatcher::add is
     used. Optional mask (or masks) can be passed to specify which query and training descriptors can be
     matched. Namely, queryDescriptors[i] can be matched with trainDescriptors[j] only if
     mask.at&lt;uchar&gt;(i,j) is non-zero.</dd>
</dl>
</li>
</ul>
<a name="match-org.opencv.core.Mat-org.opencv.