[R] recursive function

[Robert Baer]

Perhaps this is useful:
> x=c(-2,0,2)
> sign(x)*abs(x)
[1] -2  0  2


------------------------------------------
Robert W. Baer, Ph.D.
Professor of Physiology
Kirksville College of Osteopathic Medicine
A. T. Still University of Health Sciences
800 W. Jefferson St.
Kirksville, MO 63501
660-626-2322
FAX 660-626-2965



------------------------------------------
Robert W. Baer, Ph.D.
Professor of Physiology
Kirksville College of Osteopathic Medicine
A. T. Still University of Health Sciences
800 W. Jefferson St.
Kirksville, MO 63501
660-626-2322
FAX 660-626-2965


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From: "Tremblay, Pierre-Olivier" <potremblay at pharmanet.com>
Sent: Thursday, May 19, 2011 2:42 PM
To: <r-help at r-project.org>
Subject: [R] recursive function

> 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
>
> Pierre-Olivier
>
>
> [[alternative HTML version deleted]]
>
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