在R中，避免循环或套用或套用

Question

In the following code, for matrix Ma, the standard normal random vector x1 is multiplied and the column sums and maximum are obtained. By repeating this process S=1000 times, I am interested find the upper 95% quantile of f2. Due to the high dimensional matrices, it took a lot of and when I tried lapply with some modifications, I got an error message about memory allocation. Is there anyway to make this simulation faster? Thanks in advance.

set.seed(1)
S=1000; n=1000; D=10000

Ma=matrix(rnorm(n*D),ncol=D)
f2<-NULL

for (i in 1:S){
x1=rnorm(n,0,1)
f1=colSums(Ma*x1)
f2[i]=max(f1)
}

q=quantile(f2,0.95)

Answer 1

This question is just a minor variation of your previous question. The following is equivalent.

set.seed(1)
S <- n <- 1000
D <- 10000

Ma <- matrix(rnorm(n*D),ncol=D)
x1 <- matrix(rnorm(n*S,0,1),ncol=S)
f1 <- crossprod(Ma,x1)
f2 <- apply(f1,2,max)
q <- quantile(f2,0.95)