public Matrix multSlow(Matrix m) {
    Matrix n = new Matrix();
    for (int c = 0; c != 4; c++) {
      for (int r = 0; r != 4; r++) {
        float v = 0;
        for (int k = 0; k != 4; k++)
          v += get(k, r) * m.get(c, k);
        n.set(c, r, v);
      }
    }
    return n;
  }