docs: public static void fillGaussian(DMatrixD1 mat , double mean , double stdev , Random rand )
      {
          double d[] = mat.getData();
          int size = mat.getNumElements();
  
          for( int i = 0; i < size; i++ ) {
              d[i] = mean + stdev * (double)rand.nextGaussian();
          }
      }