[R] Modifying Internal C Files

[Prof Brian Ripley]

In your first post you said you called .C.  Here you say you call 
.Internal.  Users cannot add .Internal functions, nor can they be used in 
packages. In any case, The syntax is not as you show, but

     .Internal(pnbeta(q, shape1, shape2, ncp, lower.tail, log.p))

(And to be definite, that calls the C function do_math4, not pnbeta.)

Final comment:  Duncan mentioned

>> double pnbeta2(double x, double a, double b, double lambda,
>>           int lower_tail, int log_p)

but a .C call has to be to a function with all arguments as pointers, so 
there would need a wrapper function.

The reason you are finding this difficult is that you are not dealing with 
the C function behind .Internal, but one deeper into the system. The 
simplest thing to do would be to compile R from the sources, then make 
modifications and rebuild.  But in this case I believe Thomas Lumley has 
already modified the R-devel sources and Duncan Murdoch has provided 
Windows binaries of R-devel, so perhaps there is a much simpler route?


On Mon, 7 Nov 2005, Ken Kelley wrote:

> Hi Duncan and others.
>
> Thanks for your insight. Actually, I did change the function name in the
> pnbeta2.c code (I should have said so). When I check the package I get
> no errors. I build the package and all seems well. When I install and
> then load the package in R, I get:
>
> > pnbeta2
> function (x, a, b, lambda, low.tail, log.p)
> {
>     res <- .Internal("pnbeta2", as.double(x), as.double(a),
> as.double(b), as.double(lambda), as.integer(low.tail), as.integer(log.p))
>     return(list(res))
> }
> <environment: namespace:try>
>
> which seems good, but the function does not work:
>
> pnbeta2(.1, 10, 25, 2, TRUE, FALSE)
> Error in pnbeta2(0.1, 10, 25, 2, TRUE, FALSE) :
>         7 arguments passed to '.Internal' which requires 1
>
> When I try to run the .Internal file directly is perhaps where my
> problems begin:
> > .Internal(pnbeta2(.1, 10, 25, 2, TRUE, FALSE))
> Error in .Internal(pnbeta2(0.1, 10, 25, 2, TRUE, FALSE)) :
>         no internal function "pnbeta2"
>
> But, when I do the same thing to the pnbeta internal function (which
> pnbeta2 is identical to at this point) I get the result:
> > .Internal(pnbeta(.1, 10, 25, 2, TRUE, FALSE))
> [1] 0.0006837318
>
> So, I'm at a loss for what is going on in this situation. my pnbeta2
> internal function doesn't seem to be there. What I want to do is simple
> (modify an interal C file), but it is proving to be quite difficult for
> me to implement.
>
> Thanks for any thoughts,
> Ken
>
>
> Duncan Murdoch wrote:
>> On 11/7/2005 5:17 PM, Ken Kelley wrote:
>>
>>> Hi All.
>>> I want to tweak a few minor things inside of internal C code. I have
>>> my Win. XP machine set-up to build packages (including C code), but
>>> I'm having problems getting the package to run correctly. In
>>> particular, I want to modify a few things inside of pnbeta.c (namely
>>> errmax and itrmax), which is what the pbeta() function calls upon when
>>> there is a noncentral parameter. I copied the pnbeta.c C code, changed
>>> its name [to pnbeta2.c], included the nmath.h, dpq.h files, lgamma.c,
>>> and pbeta.c in my src folder (since the .h files were called upon and
>>> the .c files were). I then created an R function that I thought would
>>> call upon the new C code:
>>>
>>> pnbeta2 <- function(x, a, b, lambda, low.tail, log.p)
>>> {
>>> res <- .C("pnbeta2", as.double(x), as.double(a), as.double(b),
>>> as.double(lambda), as.integer(low.tail), as.integer(log.p))
>>> return(list(res))
>>> }
>>>
>>> But after I built the package and loaded it it, the function doesn't
>>> work (it isn't even recognized). I have no idea why this is failing.
>>> Any information to help me figure out what I need to do to modify
>>> internal C code generally, or specifically as it applies to this
>>> scenario would be most helpful.
>>
>>
>> You didn't say that you changed the name of the function, only the file
>> that contained it.  If this wasn't an oversight, then you should put
>>
>> double pnbeta2(double x, double a, double b, double lambda,
>>           int lower_tail, int log_p)
>>
>> in the appropriate place in your pnbeta2.c file.
>>
>> The other thing you should do is to add a PACKAGE argument to your .C
>> call, just in case there is already a pnbeta2 function somewhere else
>> (or will be some day).  In fact, if you do this, there should be no need
>> to change the name of the function:  R will look in the package DLL
>> rather than R.dll to find it.  Just make sure that the name in the .C
>> call matches the declared name in the source.
>>
>> Duncan Murdoch
>>
>
> -- 
> Ken Kelley, Ph.D.
> Inquiry Methodology Program
> Indiana University
> 201 North Rose Avenue, Room 4004
> Bloomington, Indiana 47405
> http://www.indiana.edu/~kenkel
>
> ______________________________________________
> 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
>

-- 
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