# File lib/backports/1.9.2/stdlib/matrix/lup_decomposition.rb, line 78
    def det
      if (@row_size != @col_size)
        Matrix.Raise Matrix::ErrDimensionMismatch unless square?
      end
      d = @pivot_sign
      @col_size.times do |j|
        d *= @lu[j][j]
      end
      d
    end