3x3 matrix multiplication - one way to do it

matrix_mult.rb

A = [[1,2,3],[4,5,6],[7,8,9]]
B = [[0,-10,20],[-30,40,-50],[60,-70,80]]
C = Array.new(A.size) { Array.new(B.size) }

B.size.times do |row|
  B.first.size.times do |col|
    column = B.map { |r| r[col] }
    results = column.map.with_index { |item, index|  item * A[(row) % B.first.size][index] }
    C[(row) % B.size][col] = results.map { |item| item }.inject(&:+)
  end
end

puts C.inspect