How about ; m <- matrix(rnorm(9), ncol = 3) mm <- matrix(rnorm(9), ncol = 3) sum(sapply(1:3, function(i, m, mm) m[i, ] %*% mm[ ,i], m, mm))
********************************** what is the best way to calculate the trace of a product of two matrices? If A <- matrix(rnorm(48),nrow=6) B <- matrix(rnorm(48),nrow=8) Is there a better (faster, more elegant) way to compute the trace of A%*%B than sum(diag(A %*% B))? I would call the above solution inelegant because all the elements of A %*% B are calculated, when one really only needs the elements on the diagonal. It also uses %*% instead of crossprod() or trcrossprod() -- Robin Hankin Uncertainty Analyst National Oceanography Centre, Southampton European Way, Southampton SO14 3ZH, UK tel 023-8059-7743 ***************************** -- Ken Knoblauch Inserm U371 Cerveau et Vision Dept. of Cognitive Neuroscience 18 avenue du Doyen Lépine 69500 Bron France tel: +33 (0)4 72 91 34 77 fax: +33 (0)4 72 91 34 61 portable: +33 (0)6 84 10 64 10 http://www.lyon.inserm.fr/371/ ______________________________________________ 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
