How to make function perform faster?

Question

I have following function: http://i.stack.imgur.com/yXA67.png, where mu is matrix (n_X rows and n_Y columns). d_X and d_Y are distance matrices.

One way to

Answer 1

This will save you 2 name look ups and a function call (i.e. [) per loop, which is a wopping 8% faster (so really @Marat Talipov's suggestion is the way to go) :

H_mu_2 <- function(mu, d_X, d_Y){
    value <- 0
    for(i in 1:nrow(d_X))
    for(j in 1:nrow(d_Y)){
        tmp <- mu[i,j]
        for(ii in 1:nrow(d_X))
        for(jj in 1:nrow(d_Y)){
            value <- value + tmp*mu[ii,jj]*abs(d_X[i,ii]-d_Y[j,jj])
        }} 
}