title: Convert Array to Matrix
body: <p>I have an array of the length <code>m*n</code>, that stores a list of <code>double</code> element. </p>
  
  <p>How to convert it into a matrix of <code>m*n</code>?</p>
  
  <p>This is the method signature.</p>
  
  <pre><code>//returns a matrix of [m,n], given arr is of length m*n
  static double[,] ConvertMatrix(Array arr, int m, int n)
  {
  }
  </code></pre>