# [Rd] [R] Use of .Fortran

David Scott d.scott at auckland.ac.nz
Sun Jun 20 04:02:56 CEST 2010

```Thanks very much to all who replied. I went with Brian's approach, and
eventually, despite all my attempts to foul it up, I did get it to work
successfully. For the record here are the details.

The subroutine is:

subroutine SSFcoef(nmax,nu,A)
implicit double precision(a-h,o-z)
implicit integer (i-n)
integer k,i,nmax
double precision nu,A(0:nmax,0:nmax)
A(0,0) = 1D0
do k=1,nmax
do i=1,k-1
A(k,i) = (-nu+i+k-1D0)*A(k-1,i)+A(k-1,i-1)
end do
A(k,0) = (-nu+k-1D0)*A(k-1,0)
A(k,k) = 1D0
end do
return
end

This was in the file SSFcoef.f95 and was made into a dll with

R CMD SHLIB SSFcoef.f95

Then calling it in R went like this:

### Load the compiled shared library in.

### Write a function that calls the Fortran subroutine
SSFcoef <- function(nmax, nu){
.Fortran("SSFcoef",
as.integer(nmax),
as.double(nu),
A = matrix(0, nmax+1, nmax+1)
)\$A
}

SSFcoef(10,2)

There are a number of comments I should make.

Yes, Brian, should have gone to R-devel. I had forgotten about that.

I recognised from my faintly recalled past Fortran experience that the
code was different and suspected a later Fortran, so good to be advised
it was 95.

I actually gave a wrong version of the Fortran subroutine, one I had
been messing around with and had added some extra arguments (nrowA and
ncolA). As pointed out these were unnecessary.

Something which then caused me a bit of grief before I noticed it.
Despite the 'implicit integer (i-n)' declaration in the subroutine, nu
is later declared to be double so has to be specified as double in the R
code.

Many thanks again, I at least learnt something about calling other
language code from R.

David

Prof Brian Ripley wrote:
> On Sat, 19 Jun 2010, David Scott wrote:
>
>> I have no experience with incorporating Fortran code and am probably doing
>> something pretty stupid.
>
> Surely you saw in the posting guide that R-help is not the place for
> questions about C, C++, Fortran code?  Diverting to R-devel.
>
>> I want to use the following Fortran subroutine (not written by me) in the
>
> Well, it is not Fortran 77 but Fortran 95, and so needs to be given a
> .f95 extension to be sure to work.
>
>> file SSFcoef.f
>>
>>      subroutine SSFcoef(nmax,nu,A,nrowA,ncolA)
>>      implicit double precision(a-h,o-z)
>>      implicit integer (i-n)
>>      integer l,i,nmax
>>      double precision nu,A(0:nmax,0:nmax)
>>      A(0,0) = 1D0
>>      do l=1,nmax
>>      	do i=1,l-1
>>      		A(l,i) = (-nu+i+l-1D0)*A(l-1,i)+A(l-1,i-1)
>>      	end do
>>      	A(l,0) = (-nu+l-1D0)*A(l-1,0)
>>      	A(l,l) = 1D0
>>      end do
>>      return
>>      end
>>
>>
>> I created a dll (this is windows) using R CMD SHLIB SSFcoef.f
>>
>> Then my R code is:
>>
>> ### Load the compiled shared library in.
>>
>> ### Write a function that calls the Fortran subroutine
>> SSFcoef <- function(nmax, nu){
>>  .Fortran("SSFcoef",
>>           as.integer(nmax),
>>           as.integer(nu)
>>           )\$A
>> }
>
> That does not match.  nrowA and ncolA are unused, so you need
> SSFcoef <- function(nmax, nu){
>    .Fortran("SSFcoef",
>             as.integer(nmax),
>             as.integer(nu),
>             A = matrix(0, nmax+1, nmax+1),
>             0L, 0L)\$A
> }
>
>
>> SSFcoef(10,2)
>>
>> which when run gives
>>
>>> SSFcoef(10,2)
>> NULL
>>
>> I am pretty sure the problem is that I am not dealing with the matrix A
>> properly. I also tried this on linux and got a segfault.
>>
>> Can anyone supply the appropriate modification to my call (and possibly to
>> the subroutine) to make this work?
>>
>> David Scott
>>

--
_________________________________________________________________
David Scott	Department of Statistics
The University of Auckland, PB 92019
Auckland 1142,    NEW ZEALAND
Phone: +64 9 923 5055, or +64 9 373 7599 ext 85055
Email:	d.scott at auckland.ac.nz,  Fax: +64 9 373 7018

Director of Consulting, Department of Statistics

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