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