Creates a random set of points distributed *near* the circumference * of a circle and trains an SOM that finds that circular pattern. The * generating function is * \f{eqnarray*}{ * r &\in& [1-\delta r, 1+\delta r)\\ * \theta &\in& [0, 2\pi)\\ * x &=& r\cos\theta\\ * y &=& r\sin\theta * \f} * * \param[out] data matrix to store data in */