docs: public static double[][] timesEquals(final double[][] m1, final double s1) {
      final int rowdim = m1.length;
      for(int i = 0; i < rowdim; i++) {
        final double[] row = m1[i];
        for(int j = 0; j < row.length; j++) {
          row[j] *= s1;
        }
      }
      return m1;
    }