@Override
  public Object clone() throws CloneNotSupportedException {
    IndexingOp ret = new IndexingOp();

    // copy generic attributes
    ret.clone(this, false);

    // copy specific attributes

    return ret;
  }
  /**
   * @param c
   * @param vars
   * @return
   * @throws DMLRuntimeException
   */
  private static LiteralOp replaceLiteralFullUnaryAggregateRightIndexing(
      Hop c, LocalVariableMap vars) throws DMLRuntimeException {
    LiteralOp ret = null;

    // full unary aggregate w/ indexed matrix less than 10^6 cells
    if (c instanceof AggUnaryOp
        && isReplaceableUnaryAggregate((AggUnaryOp) c)
        && c.getInput().get(0) instanceof IndexingOp
        && c.getInput().get(0).getInput().get(0) instanceof DataOp) {
      IndexingOp rix = (IndexingOp) c.getInput().get(0);
      Hop data = rix.getInput().get(0);
      Hop rl = rix.getInput().get(1);
      Hop ru = rix.getInput().get(2);
      Hop cl = rix.getInput().get(3);
      Hop cu = rix.getInput().get(4);

      if (data instanceof DataOp
          && vars.keySet().contains(data.getName())
          && isIntValueDataLiteral(rl, vars)
          && isIntValueDataLiteral(ru, vars)
          && isIntValueDataLiteral(cl, vars)
          && isIntValueDataLiteral(cu, vars)) {
        long rlval = getIntValueDataLiteral(rl, vars);
        long ruval = getIntValueDataLiteral(ru, vars);
        long clval = getIntValueDataLiteral(cl, vars);
        long cuval = getIntValueDataLiteral(cu, vars);

        MatrixObject mo = (MatrixObject) vars.get(data.getName());

        // get the dimension information from the matrix object because the hop
        // dimensions might not have been updated during recompile
        if (mo.getNumRows() * mo.getNumColumns() < REPLACE_LITERALS_MAX_MATRIX_SIZE) {
          MatrixBlock mBlock = mo.acquireRead();
          MatrixBlock mBlock2 =
              mBlock.sliceOperations(
                  (int) (rlval - 1),
                  (int) (ruval - 1),
                  (int) (clval - 1),
                  (int) (cuval - 1),
                  new MatrixBlock());
          double value = replaceUnaryAggregate((AggUnaryOp) c, mBlock2);
          mo.release();

          // literal substitution (always double)
          ret = new LiteralOp(value);
        }
      }
    }

    return ret;
  }
  /**
   * @param c
   * @param vars
   * @return
   * @throws DMLRuntimeException
   */
  private static LiteralOp replaceLiteralValueTypeCastRightIndexing(Hop c, LocalVariableMap vars)
      throws DMLRuntimeException {
    LiteralOp ret = null;

    // as.scalar/right indexing w/ literals/vars and matrix less than 10^6 cells
    if (c instanceof UnaryOp
        && ((UnaryOp) c).getOp() == OpOp1.CAST_AS_SCALAR
        && c.getInput().get(0) instanceof IndexingOp
        && c.getInput().get(0).getDataType() == DataType.MATRIX) {
      IndexingOp rix = (IndexingOp) c.getInput().get(0);
      Hop data = rix.getInput().get(0);
      Hop rl = rix.getInput().get(1);
      Hop ru = rix.getInput().get(2);
      Hop cl = rix.getInput().get(3);
      Hop cu = rix.getInput().get(4);
      if (rix.dimsKnown()
          && rix.getDim1() == 1
          && rix.getDim2() == 1
          && data instanceof DataOp
          && vars.keySet().contains(data.getName())
          && isIntValueDataLiteral(rl, vars)
          && isIntValueDataLiteral(ru, vars)
          && isIntValueDataLiteral(cl, vars)
          && isIntValueDataLiteral(cu, vars)) {
        long rlval = getIntValueDataLiteral(rl, vars);
        long clval = getIntValueDataLiteral(cl, vars);

        MatrixObject mo = (MatrixObject) vars.get(data.getName());

        // get the dimension information from the matrix object because the hop
        // dimensions might not have been updated during recompile
        if (mo.getNumRows() * mo.getNumColumns() < REPLACE_LITERALS_MAX_MATRIX_SIZE) {
          MatrixBlock mBlock = mo.acquireRead();
          double value = mBlock.getValue((int) rlval - 1, (int) clval - 1);
          mo.release();

          // literal substitution (always double)
          ret = new LiteralOp(value);
        }
      }
    }

    return ret;
  }