Hi, Suppose I have a vector in real number (x1, x2, x3, x4, x5, x6) My question is how I can get x5*x3*x1 + x6*x4*x2 ? Thanks a lot. Dot. -- View this message in context: http://www.nabble.com/how-can-I-do-this-sum--tp18931693p18931693.html Sent from the R help mailing list archive at Nabble.com.