CODEWITHSUNDEEP
rfunctionloopsmatrix
Prad
Prad

Reputation: 339

multiplying matrices with reference matrix n times

x is the reference matrix for all the iterations. there are total 2 matrices. 

matrix A
1   4   1   4
4   2   4   2
2   3   2   3
3   3   3   3

matrix B
1   4   1   4
4   2   4   2
2   3   2   3
3   3   3   3


matrix x
4   1   4   3
2   4   2   2
3   2   3   5
3   5   1   1

Here matrix A and B is same. We need a matrix multiplication in the below fasion: 

C <- B %*% x
D <- C %*% x
E <- D %*% x 
F <- E %*% x

x is the reference matrix for all the iterations. this multiplication is done for 15 times so need help in writting in a loop or function.

Upvotes: 1

Views: 783

Answers (1)

Florian
Florian

Reputation: 25425

If you only want the last matrix we can use a recursive function, as suggested by Sotos:

A <- matrix(runif(9), 3) 
X <- matrix(runif(9), 3) 

repmult <- function(A,x,reps)
{
  if(reps==0){
    return(A)
  }
  else
  {
    repmult(A%*%x,x,reps-1)
  }
}

repmult(A,X,15)

If you want all intermediate results in a list as well, we can modify the function from the answer on this SO question (although you may want to change its name):

Mpow <- function(A,x, n) {
  L <- list(A%*%x)
  if (n==1) return(L)
  P <- A
  for (i in 1:n) L[[i]] <- (P <- P %*% x)
  return(L)
}

Mpow(A,X,3)

Upvotes: 2

Related Questions