> -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-bounces@r- > project.org] On Behalf Of wilkesma > Sent: Thursday, November 08, 2012 5:49 AM > To: r-help@r-project.org > Subject: [R] Looping matrix multiplication > > I am dealing with a number of time-series consisting of 2250 samples of > flow > velocity in 2D (Vx, Vy). > > For each time-series I have determined the resultant vector angle (d) > and > magnitude (Vres) based on the ensemble means of Vx and Vy and now want > to > rotate each point in the time-series by d so that mean(Vx)=Vres and > mean(Vy)=0. > > Here is the code I have written to perform the rotation for a single > time-step: > > n <- 2250 #number of samples in time series > R <- matrix ((c ((cos(d)), (-sin(d)), (sin(d)), (cos(d)))), 2) > #rotation > matrix, where d is the resultant vector angle in degrees > V <- t (matrix ((c (Vx, Vy)), n)) #velocity matrix > Vadj <- R %*% (V) [, 1] #e.g. for the first Vx, Vy pair in the time- > series > > Now what I want to do is loop this to give me the solution at each > time-step > and then append the adjusted Vx and Vy time-series to a new matrix. > Can > someone please suggest how I should about this? > > Thanks, > Martin > >
Perhaps the following will get what you want Vadj <- V %*% t(R) Hope this is helpful, Dan Daniel Nordlund Olympia, WA 98504-5204 ______________________________________________ R-help@r-project.org 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.
