nrowx <- 100000
ncolx <- 100
nrep <- 100
 
 x<-matrix(1, nrowx, ncolx)
 y<-1 : ncolx
 
 m1 <- function (x, y) { x %*% diag (y) }
 cat("matrix multiplication    ", formatC(system.time(gcFirst=TRUE, for (i in 1:nrep) m1(x,y))[1:3], digits=6), "\n")
 m2 <- function (x, y) { tcrossprod (x, diag(y)) }
 cat("tcrossprod               ", formatC(system.time(gcFirst=TRUE, for (i in 1:nrep) m2(x,y))[1:3], digits=6), "\n")
 m3 <- function (x, y) { t (y * t(x)) }
 cat("transposition and reuse  ", formatC(system.time(gcFirst=TRUE, for (i in 1:nrep) m3(x,y))[1:3], digits=6), "\n")
 m4 <- function (x, y) { x * matrix (y, nrowx, ncolx, byrow = TRUE) }
 cat("elementwise after reshape", formatC(system.time(gcFirst=TRUE, for (i in 1:nrep) m4(x,y))[1:3], digits=6), "\n")
 m5 <- function (x, y) { sapply (1 : ncolx, function (i) x[, i] * y[i]) }
 cat("columnwise sapply  ", formatC(system.time(gcFirst=TRUE, for (i in 1:nrep) m5(x,y))[1:3], digits=6), "\n")
 m6 <- function (x, y) { for (i in 1:ncolx) { x[,i] <- x[, i] * y[i]  }; return (x) }
 cat("for loop over columns    ", formatC(system.time(gcFirst=TRUE, for (i in 1:nrep) m6(x,y))[1:3], digits=6), "\n")