Thanks, Berend. I updated my R and got same result. I reposted the old sessionInfo(), which was an older version. But, same code, same matrices, different result
> -----Original Message----- > From: Berend Hasselman [mailto:b...@xs4all.nl] > Sent: Tuesday, August 14, 2012 1:49 PM > To: Doran, Harold > Cc: 'r-help@r-project.org' > Subject: Re: [R] Communative Matrix Multiplcation > > > On 14-08-2012, at 19:26, Doran, Harold wrote: > > > > > I'm not seeing why the following occurs: > > > >> T1 <- (A1 - A2) %*% D > >> T2 <- (A1 %*% D) - (A2 %*% D) > >> identical(T1, T2) > > [1] FALSE > > ....... > > I ran this in a clean environment > > <code> > library(Matrix) > > A1 <- new("dsCMatrix" > , i = c(0L, 1L, 2L, 3L, 0L, 1L, 4L, 2L, 3L, 5L) > , p = c(0L, 1L, 2L, 3L, 4L, 7L, 10L) > , Dim = c(6L, 6L) > , Dimnames = list(NULL, NULL) > , x = c(5, 5, 5, 5, 5, 5, 10, 5, 5, 10) > , uplo = "U" > , factors = list() > ) > > A2 <- new("dgeMatrix" > , x = c(1.41313955042629, 1.23647532592053, 1.36413787785255, > 0.986247245800629, 2.64961487634682, 2.35038512365318, 1.23647532592053, > 1.55872699943971, 0.579347997632991, 1.62544967700677, 2.79520232536024, > 2.20479767463976, 1.36413787785255, 0.579347997632991, 2.75106274522123, > 0.305451379293231, 1.94348587548554, 3.05651412451446, 0.986247245800629, > 1.62544967700677, 0.305451379293232, 2.08285169789937, 2.6116969228074, > 2.3883030771926, 2.64961487634682, 2.79520232536024, 1.94348587548554, > 2.6116969228074, 5.44481720170706, 4.55518279829294, 2.35038512365318, > 2.20479767463976, 3.05651412451446, 2.3883030771926, 4.55518279829294, > 5.44481720170706 > ) > , Dim = c(6L, 6L) > , Dimnames = list(NULL, NULL) > , factors = list() > ) > > D <- new("ddiMatrix" > , diag = "N" > , Dim = c(6L, 6L) > , Dimnames = list(NULL, NULL) > , x = c(5, 5, 5, 5, 10, 10) > ) > > A1 > A2 > D > > T1 <- (A1 - A2) %*% D > T2 <- (A1 %*% D) - (A2 %*% D) > identical(T1, T2) > </code> > > and qot this result > > [1] TRUE > > > so it's now up to you to find out what you did exactly. > > Berend ______________________________________________ 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.
