function _column(value, column) {
    // check dimensions
    if (value.size().length !== 2) {
      throw new Error('Only two dimensional matrix is supported');
    }

    validateIndex(column, value.size()[1]);
    var rowRange = range(0, value.size()[0]);
    var index = new MatrixIndex(rowRange, column);
    return value.subset(index);
  }
Retrieve a column of a matrix
@param {Matrix } value  A matrix
@param {number} column  The index of the column
@return {Matrix}        The retrieved column