In the tutorial at http://opencv.itseez.com/doc/tutorials/ml/introduction_to_svm/introduction_to_svm.html, there is a small bug in the code.

On line 15:
<pre><code class="cpp">
"Mat labelsMat(3, 1, CV_32FC1, labels);"
</code></pre>

should be
<pre><code class="cpp">
"Mat labelsMat(4, 1, CV_32FC1, labels);"
</code></pre>

On line 18:
<pre><code class="cpp">
"Mat trainingDataMat(3, 2, CV_32FC1, trainingData);"
</code></pre>

should be
<pre><code class="cpp">
"Mat trainingDataMat(4, 2, CV_32FC1, trainingData);"
</code></pre>

The same bugs appear in part 1 of the explanation.