[R] code optimization tips

[baptiste Auguié]

Thanks for your reply,

On 23 Jul 2007, at 15:19, jim holtman wrote:

> First question is why are you defining the functions within the main
> function each time?  Why don't you define them once outside?
>


Fair enough!

As said, I'm new to R and don't know whether it is best to define  
functions outside and pass to them all necessary arguments, or nest  
them and get variables in the scope from parents. In any case, I'd  
agree my positions(), mod() and sij() functions would be better  
outside. Here is a corrected version (untested as something else is  
running),

>
> positions <- function(N) {
>    reps <- 2*N+1
>    matrix(c(rep(-N:N, each = reps), rep(-N:N, times = reps)),
>           nrow = 2, byrow = TRUE)
> }

> mod<-function(x){sqrt(x[1]^2+x[2]^2)} # modulus

> sij <-function(rj,ri,k){
> rij=mod(rj-ri)
> cos_ij=rj[1]/rij
> sin_ij=rj[2]/rij
>
> A<-(1-1i*k*rij)*(3*cos_ij^2-1)*exp(1i*k*rij)/(rij^3)
> B<-k^2*sin_ij^2*exp(1i*k*rij)/rij
>
> sij<-A+B
> }

> alpha_c <- function(lambda=600e-9,alpha_s=1e-14,N=400,spacing=1e-7){
>
> k<-2*pi/lambda
> ri<-c(0,0) # particle at the origin
>
> rj<-positions(N)*spacing # all positions in the 2N x 2N array
> rj<-rj[1:2,-((dim(rj)[2]-1)/2+1)] # remove rj=(0,0)
>
> s_ij<-apply(rj,2,sij)

*** Now, how do I pass k and ri to this function ? ***

> S<-sum(s_ij)
> alpha_s/(1-alpha_s*S)
> }
> alpha_c()
>


>
> -- 
> Jim Holtman
> Cincinnati, OH
> +1 513 646 9390
>
> What is the problem you are trying to solve?


Wondering whether that's part of the signature?

the problem is related to scattering by arrays of particles, more  
specifically to evaluate the array influence on the effective  
polarizability (alpha) of a particle via dipolar radiative coupling.