rank_e

# File lib/matrix.rb, line 828
  def rank_e
    a = to_a
    a_column_size = column_size
    a_row_size = row_size
    pi = 0
    (0 ... a_column_size).each do |j|
      if i = (pi ... a_row_size).find{|i0| !a[i0][j].zero?}
        if i != pi
          a[pi], a[i] = a[i], a[pi]
        end
        (pi + 1 ... a_row_size).each do |k|
          q = a[k][j].quo(a[pi][j])
          (pi ... a_column_size).each do |j0|
            a[k][j0] -= q * a[pi][j0]
          end
          if k > pi && !a[k][j].zero?
            a[k], a[pi] = a[pi], a[k]
            redo
          end
        end
        pi += 1
      end
    end
    pi
  end