title: OpenCV Help - Error: no match for ‘operator[]’ (operand types are ‘cv::Mat’ and ‘int’)
body: <p>In OpenCV 2.4.10 I want to convert a row matrix to a matrix 12x12:</p>
  
  <pre><code>//Extraction SIFT
    SiftDescriptorExtractor extractor;
    Mat descriptors_1, descriptors_2;
    extractor.compute( img_1, keypoints_1, descriptors_1);
    extractor.compute( img_2, keypoints_2, descriptors_2);
  
    Mat matrix(12,12, CV_8UC3, Scalar(0));
    int j = 0;
    for (int x = 0; x&lt;12; x++)
    {
       for (int y = 0; y&lt;12; y++)
       {
        matrix [x][y] = descriptors_2[x][j];
        j++
  
       }
  
    }
  </code></pre>
  
  <p>The error on line 67 <code>no match for ‘operator[]’ (operand types are ‘cv::Mat’ and ‘int’)</code>.
  Can anyone help me? Thanks. </p>