Dear R people, I do not have much knowledge about linear algebra but currently I need to understand what the function qr.qty is actually doing. The documentation states that it calculates t(Q) %*% y via a previously performed QR matrix decomposition.
In order to do that, I tried following basic example: m<-matrix(c(1,0,0,0,1,0,0,0,1,0,0,1),ncol=3) # 4x3 matrix qr.qty(qr(m),matrix(c(1,2,3,4,2,3,4,5,1,1,1,1,2,2,2,2),nrow=4)) [,1] [,2] [,3] [,4] [1,] -1 -2 -1 -2 [2,] -4 -5 -1 -2 [3,] 3 4 1 2 [4,] -2 -3 -1 -2 As far as I understood the documentation a call such as t(qr.Q(qr(m)))%*%matrix(c(1,2,3,4,2,3,4,5,1,1,1,1,2,2,2,2),nrow=4) should produce the same result, but this produces a 3 by 4 rather than a four by four matrix as t(qr.Q(qr(m))) has only three rows. [,1] [,2] [,3] [,4] [1,] -1 -2 -1 -2 [2,] -4 -5 -1 -2 [3,] 3 4 1 2 So the last line is missing. Any hints how R adds the last line would be appreciated. Regards, Sebastian ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.