code: public static DMatrixRMaj diagonal(int N , double min , double max , Random rand ) {
          return diagonal(N,N,min,max,rand);
      }
docs: Creates a random diagonal matrix where the diagonal elements are selected from a uniform
  distribution that goes from min to max.
  
  @param N Dimension of the matrix.
  @param min Minimum value of a diagonal element.
  @param max Maximum value of a diagonal element.
  @param rand Random number generator.
  @return A random diagonal matrix.