R help - Sep 2006 - Retrieving value computed in inner function call

Dear R users,

Consider the following example function:

f = function(a,b) {
    g = function(x) a*x + b
    h = function(x) g(x)^2 + x^2
    opt = optimize(h,lower = -1, upper = 1)
    x.min = opt$minimum
    h.xmin = opt$objective
    g.xmin = g(x.min)
    return(c(x.min, h.xmin, g.xmin))
}

In my real problem the function that plays the role of "g" is costly 
to compute. Now, to minimize "h", "optimize" calls
"h" with different
values of x. In particular, at the end of the optimization, "h" would 
be called with argument x.min, the minimizer of h(x). Therefore, 
buried somewhere, there has to be a call to "g" with argument x=x.min 
which I would like to retrieve in order to avoid the extra call to 
"g" in the line before the return. Can this be done without too much
pain?

I'd very much appreciate any help.



Juan Pablo Lewinger
Department of Preventive Medicine
University of Southern California

Check out:

http://finzi.psych.upenn.edu/R/Rhelp02a/archive/83547.html

On 9/12/06, Juan Pablo Lewinger <lewinger at usc.edu>
wrote:
> Dear R users,
>
> Consider the following example function:
>
> f = function(a,b) {
>    g = function(x) a*x + b
>    h = function(x) g(x)^2 + x^2
>    opt = optimize(h,lower = -1, upper = 1)
>    x.min = opt$minimum
>    h.xmin = opt$objective
>    g.xmin = g(x.min)
>    return(c(x.min, h.xmin, g.xmin))
> }
>
> In my real problem the function that plays the role of "g" is
costly
> to compute. Now, to minimize "h", "optimize" calls
"h" with different
> values of x. In particular, at the end of the optimization, "h"
would
> be called with argument x.min, the minimizer of h(x). Therefore,
> buried somewhere, there has to be a call to "g" with argument
x=x.min
> which I would like to retrieve in order to avoid the extra call to
> "g" in the line before the return. Can this be done without too
much pain?
>
> I'd very much appreciate any help.
>
>
>
> Juan Pablo Lewinger
> Department of Preventive Medicine
> University of Southern California
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

Though not obvious at first the posting you pointed me too is very helpful 
indeed. Thanks a lot Gabor.

Juan Pablo

At 08:48 PM 9/12/2006 -0400, Gabor Grothendieck wrote:
>Check out:
>
>http://finzi.psych.upenn.edu/R/Rhelp02a/archive/83547.html
>
>On 9/12/06, Juan Pablo Lewinger <lewinger at usc.edu> wrote:
>>Dear R users,
>>
>>Consider the following example function:
>>
>>f = function(a,b) {
>>    g = function(x) a*x + b
>>    h = function(x) g(x)^2 + x^2
>>    opt = optimize(h,lower = -1, upper = 1)
>>    x.min = opt$minimum
>>    h.xmin = opt$objective
>>    g.xmin = g(x.min)
>>    return(c(x.min, h.xmin, g.xmin))
>>}
>>
>>In my real problem the function that plays the role of "g" is
costly
>>to compute. Now, to minimize "h", "optimize" calls
"h" with different
>>values of x. In particular, at the end of the optimization,
"h" would
>>be called with argument x.min, the minimizer of h(x). Therefore,
>>buried somewhere, there has to be a call to "g" with argument
x=x.min
>>which I would like to retrieve in order to avoid the extra call to
>>"g" in the line before the return. Can this be done without
too much pain?
>>
>>I'd very much appreciate any help.
>>
>>
>>
>>Juan Pablo Lewinger
>>Department of Preventive Medicine
>>University of Southern California
>>
>>______________________________________________
>>R-help at stat.math.ethz.ch mailing list
>>https://stat.ethz.ch/mailman/listinfo/r-help
>>PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
>>and provide commented, minimal, self-contained, reproducible code.