title: How to set values in an OpenCV 64FC1 matrix
body: <p>I am trying to make a matrix of three rows and one column with the values 1, 2 and 3 in it. </p>
  
  <pre><code>int main(int argc, char *argv[])
  {
  
      cv::Mat point = cv::Mat::ones(3, 1, CV_64FC1);
      point.at&lt;double&gt;(1,1) = 1.0d;
      point.at&lt;double&gt;(1,2) = 2.0d;
      point.at&lt;double&gt;(1,3) = 3.0d;
      std::cout &lt;&lt; point &lt;&lt; std::endl;
  
      return 0;
  }
  </code></pre>
  
  <p>The output is:</p>
  
  <pre><code>[1
   1
   1]
  </code></pre>
  
  <p>And the expected output is:</p>
  
  <pre><code>[1
   2
   3]
  </code></pre>
  
  <p>How are values set in an OpenCV matrix?</p>