How to declare list object with M elements

Maybe this:

myls <- vector("list", length = S)

Try

mylist <- rep(list(elm),7)

which, for S=3, gives

[[1]]
     [,1] [,2] [,3]
[1,]   NA   NA   NA
[2,]   NA   NA   NA
[3,]   NA   NA   NA

[[2]]
     [,1] [,2] [,3]
[1,]   NA   NA   NA
[2,]   NA   NA   NA
[3,]   NA   NA   NA

[[3]]
     [,1] [,2] [,3]
[1,]   NA   NA   NA
[2,]   NA   NA   NA
[3,]   NA   NA   NA

By the way, identical(matrix(NA,3,3),matrix(,3,3)) is true, since matrices are initialized to NA by default. See ?matrix.