docs: public static double[] rowPackedCopy(final double[][] m1) {
      final int rowdim = m1.length, coldim = getColumnDimensionality(m1);
      final double[] vals = new double[rowdim * coldim];
      for(int i = 0, j = 0; i < rowdim; i++, j += coldim) {
        // assert m1[i].length == coldim : ERR_MATRIX_RAGGED;
        System.arraycopy(m1[i], 0, vals, j, coldim);
      }
      return vals;
    }