[R] Integration in R

[Berend Hasselman]

On 02-10-2012, at 20:01, Rui Barradas <ruipbarradas at sapo.pt> wrote:

> Hello,
> 
> Yes, it's possible to remove the loop. Since the loop is used to compute a running product and all we want is the final result, use the vectorized behavior of R and a final ?prod().
> Seedup: another 2x. And 4x2 == 8 == 1 [decimal] order of magnitude.
> 
> 
> lf2 <-function (x) {
>   v<-1
>   x1 <- x[1]
>   x2 <- x[2]
>   x3 <- x[3]
>   x4 <- x[4]
>   z1 <- exp(x1+x2*dose)
>   z2 <- exp(x3+x4*dose)
>   psi0<-1/((1+z1)*(1+z2))
>   psi1<-z1*psi0
>   v <- (psi0^y0)*(psi1^y1)*((1-psi0-psi1)^y2)
>   return( prod(v) )
> }
> 
> lf2.c <- cmpfun(lf2)
> 
> Hope this helps,


Wonderful. It certainly does help.
A single nitpick: the v <- 1 at the start of the function can now be removed.

I got a speedup of 7.5 compared to the very first version lf1.

Berend