inverse_from

# File lib/matrix.rb, line 581
  def inverse_from(src)
    size = row_size - 1
    a = src.to_a
    
    for k in 0..size
      i = k
      akk = a[k][k].abs
      ((k+1)..size).each do |j|
        v = a[j][k].abs
        if v > akk
          i = j
          akk = v
        end
      end
      Matrix.Raise ErrNotRegular if akk == 0
      if i != k
        a[i], a[k] = a[k], a[i]
        @rows[i], @rows[k] = @rows[k], @rows[i]
      end
      akk = a[k][k]
      
      for i in 0 .. size
        next if i == k
        q = a[i][k].quo(akk)
        a[i][k] = 0
        
        for j in (k + 1).. size
          a[i][j] -= a[k][j] * q
        end
        for j in 0..size
          @rows[i][j] -= @rows[k][j] * q
        end
      end
      
      for j in (k + 1).. size
        a[k][j] = a[k][j].quo(akk)
      end
      for j in 0..size
        @rows[k][j] = @rows[k][j].quo(akk)
      end
    end
    self
  end