# [Rd] Problem with function in fortran 95

Simone Giannerini sgiannerini at gmail.com
Fri Aug 14 11:19:41 CEST 2009

```Fabio,

I see two problems with your code:

1. R type numeric corresponds to FORTRAN Real*8 (or double precision)
so that line 4 of your mat.f95 becomes:

REAL*8 :: x, y, res

2. your R code won't ever succeed because you pass integer matrices
(x,y,res) to a subroutine that expects REAL*8 data.
you need to coerce all your matrices to "double" as follows:

storage.mode(x) <- "double"
storage.mode(y) <- "double"
storage.mode(res) <- "double"

Finally, you can call the corrected function:

.Fortran("mymult", x,y,res,as.integer(l),as.integer(c))
[[1]]
[,1] [,2] [,3] [,4]
[1,]    1    6   11   16
[2,]    2    7   12   17
[3,]    3    8   13   18
[4,]    4    9   14   19
[5,]    5   10   15   20

[[2]]
[,1] [,2] [,3] [,4] [,5]
[1,]   20   16   12    8    4
[2,]   19   15   11    7    3
[3,]   18   14   10    6    2
[4,]   17   13    9    5    1

[[3]]
[,1] [,2] [,3] [,4] [,5]
[1,]  604  468  332  196   60
[2,]  678  526  374  222   70
[3,]  752  584  416  248   80
[4,]  826  642  458  274   90
[5,]  900  700  500  300  100

[[4]]
[1] 5

[[5]]
[1] 4

All these issues are discussed in the "Writing R Extensions" manual,

Ciao

Simone

On Wed, Aug 12, 2009 at 1:32 PM, Fabio Mathias
Corrêa<fabio.ufla at yahoo.com.br> wrote:
> I am writing a function in fortran 95, but the intrinsic function MATMUL is not working properly. Here's an example.
>
>        SUBROUTINE mymult(x,y,res,m,n)
>        IMPLICIT NONE
>        INTEGER :: m,n
>        REAL :: x, y, res
>        DIMENSION :: x(m,n), y(n,m), res(m,m)
>        res = MATMUL(x,y)
>        END SUBROUTINE mymult
>
> R CMD SHLIB mat.f95
>
> In R:
>
> x   <- matrix(1:20,5)
> l   <- nrow(x)
> c   <- ncol(x)
> y   <- matrix(20:1,c)
> res <- matrix(0,l,l)
> dim(x)
> dim(y)
> dim(res)
> l
> c
> .Fortran("mymult", x,y,res,l,c)
>
> [[1]]
>     [,1] [,2] [,3] [,4]
> [1,]    1    6   11   16
> [2,]    2    7   12   17
> [3,]    3    8   13   18
> [4,]    4    9   14   19
> [5,]    5   10   15   20
>
> [[2]]
>     [,1] [,2] [,3] [,4] [,5]
> [1,]   20   16   12    8    4
> [2,]   19   15   11    7    3
> [3,]   18   14   10    6    2
> [4,]   17   13    9    5    1
>
> [[3]]
>     [,1] [,2] [,3] [,4] [,5]
> [1,]    0    0    0    0    0
> [2,]    0    0    0    0    0
> [3,]    0    0    0    0    0
> [4,]    0    0    0    0    0
> [5,]    0    0    0    0    0
>
> [[4]]
> [1] 5
>
> [[5]]
> [1] 4
>
>
> Linux Ubuntu 8.04 and use compiler gfortran 4.2.
> The problem is the compiler?
>
> Thanks!
>
>                Fábio Mathias Corrêa
> Estatística e Experimentação Agropecuária/UFLA
>                      Brazil
>
>
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>
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--
______________________________________________________

Simone Giannerini
Dipartimento di Scienze Statistiche "Paolo Fortunati"
Universita' di Bologna
Via delle belle arti 41 - 40126  Bologna,  ITALY
Tel: +39 051 2098262  Fax: +39 051 232153
http://www2.stat.unibo.it/giannerini/

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