inverse_from(src) private

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# File lib/matrix.rb, line 1066
  def inverse_from(src) # :nodoc:
    last = row_count - 1
    a = src.to_a

    0.upto(last) do |k|
      i = k
      akk = a[k][k].abs
      (k+1).upto(last) 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]

      0.upto(last) do |ii|
        next if ii == k
        q = a[ii][k].quo(akk)
        a[ii][k] = 0

        (k + 1).upto(last) do |j|
          a[ii][j] -= a[k][j] * q
        end
        0.upto(last) do |j|
          @rows[ii][j] -= @rows[k][j] * q
        end
      end

      (k+1).upto(last) do |j|
        a[k][j] = a[k][j].quo(akk)
      end
      0.upto(last) do |j|
        @rows[k][j] = @rows[k][j].quo(akk)
      end
    end
    self
  end
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