[R] integrate a function in R

[Prof Brian Ripley]

Where is the lexical scoping in this solution?  Your one function is
defined in the global environment, and `u' just happens to be too (unlike 
C and another implementation of the S language).

Even if it were relevant, it seems to obscure what is going on.  Compare

zfz <- function(z, mu) z*dnorm(x=z, mean=mu)
for(i in seq(along=us)) {
    u <- us[i]
    out[i] <- integrate(zfz, 0, u+3, mu=u)$value
}

which is easier to follow and is less error-prone (even if you need to
ensure that `u' does not match `upper').  When I use lexical scoping to
capture variables I normally add a note in the code to remind readers.  
Otherwise someone will streamline the code to

for(i in seq(along=us)) out[i] <- integrate(zfz, 0, us[i]+3)$value


On Thu, 28 Oct 2004, Dimitris Rizopoulos wrote:

> Hi Liu,
> 
> you should take advantage of lexical scoping, i.e.,
> 
> 
> zfz <- function(z) z*dnorm(x=z, mean=u)
> us <- seq(-1, 1, length=10)
> out <- numeric(length(us))
> for(i in seq(along=us)){
>     u <- us[i]
>     out[i] <- integrate(zfz, 0, u+3)$value
> }
> out
> 
> 
> I hope it helps.
> 
> Best,
> Dimitris
> 
> ----
> Dimitris Rizopoulos
> Ph.D. Student
> Biostatistical Centre
> School of Public Health
> Catholic University of Leuven
> 
> Address: Kapucijnenvoer 35, Leuven, Belgium
> Tel: +32/16/396887
> Fax: +32/16/337015
> Web: http://www.med.kuleuven.ac.be/biostat/
>      http://www.student.kuleuven.ac.be/~m0390867/dimitris.htm
> 
> 
> ----- Original Message ----- 
> From: "yyan liu" <zhliur at yahoo.com>
> To: <r-help at stat.math.ethz.ch>
> Sent: Thursday, October 28, 2004 12:56 AM
> Subject: [R] integrate a function in R
> 
> 
> > Hi:
> >  I want to integrate the following function with
> > respect to "z", "u" is another argument in the
> > function. My program is a loop and in each loop the
> > argument "u" will be given a specified numeric values.
> > But how can I use the "integrate" function with "u" in
> > R?
> >  The function is:
> > zfz<-function(z,u)
> > {
> >  return(z*dnorm(z,u,1) )
> > }
> >
> > And in each loop, the integration interval is [0,u+3].
> > I can not just use integrate(zfz,0,u+3) because "u"
> > can not be specified.
> > Thank you!
> >
> > liu
> >
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595