[R] Using functions that contain sums

[Charles C. Berry]

On Fri, 26 Sep 2008, Patrick M. Joyce wrote:

> Hello,
>
> I'm trying to perform an integration on a function that contains a sum.
> Similarly I'm hoping whatever acts as a fix will be good enough to aid in
> a 2nd case as well but I've already put in a work-around for that
> situation.
>
> My code example is here:
>
> watermelon=c(0,1,2,3)
>
> w<-function(x){
> sum(sin(x-watermelon))}
>
> integrate(function(x){w(x)},0,2)
>
> integrate(function(x){sin(x)+sin(x-1)+sin(x-2)+sin(x-3)},0,2)
>
> the first integral gives an error... the 2nd is what I should get for an
> answer for the first.  Is there a way to get this to work the way that I
> desire?

Yes.

Do as you were asked:

 	*) Read the Posting Guide

 	Note this bit:

 		Do your homework before posting ...

 		    * Read the online help for relevant functions (type ?functionname,

 	*) Then read the documentation for 'integrate'

 	Note this bit:

 		   f must accept a vector of inputs and produce a vector
                    of function evaluations at those points. The Vectorize
                    function may be helpful to convert f to this form.

You may find the functions 'outer' and 'rowSums' to be helpful in crafting 
a version of 'f' that produces vectorized output in this case.

HTH,

Chuck

>
> Any help is appreciated.
>
> Sincerely,
> Patrick Joyce
>
> ______________________________________________
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> and provide commented, minimal, self-contained, reproducible code.
>

Charles C. Berry                            (858) 534-2098
                                             Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu	            UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego 92093-0901