[R] recursive function

[Rolf Turner]

(1) What has this to do with recursion?

(2) You probably need to use ifelse().  I believe that this is
(in effect) an FAQ.

     cheers,

         Rolf Turner

On 20/05/11 07:42, Tremblay, Pierre-Olivier wrote:
> Hi,
>
> I created a function for obtaining the normal cumulative distribution (I
> know all this already exists in R, I just wanted to verify my
> understanding of it).  below is the code I came up with.
>
> cdf<-function(x) {
>          erf<-function(x) {
>             # approximation to the error function (erf) of the
>             # normal cumulative distribution function
>             # from Winitzki (2008)
>                a<- 0.147
>                partc<- 1+a*x^2
>                partb<- 4/pi+a*x^2
>                parta<- -x^2*(partb/partc)
>                erf<- sqrt(1-exp(parta))
>                erf
>                   }
>      #  cumulative density function
>        cdf<- 1/2*(1+erf(x/sqrt(2)))
>        cdf
>      }
>
> The erf(x) produces positive values whatever the sign of x.  Instead of
> obtaining the expected sigmoid shape of the erf() I end up with a
> positive values V shape.  erf(x) should be negative for negative values
> of x.  I figure I need some form of conditional statement in the above
> code but all my attempts at using "if" and "for" failed miserably.
> Clearly, I don't understand how to use them properly in R.  If anyone
> could point me in the right direction as on how to code conditional
> events in R that would be much appreciated.
>
> many thanks in advance