1 2 3 4 5
4.times{|i| col = i+1 row = i+1 print "m1._2#{col} * m2._#{row}1 + " }
1
m1._21 * m2._11 + m1._22 * m2._21 + m1._23 * m2._31 + m1._24 * m2._41 +