[R] the use of the .C function

[Bernardo Lagos Alvarez]

Dear All,
could someone please shed some light on the use of the .C  or .Fortran function:


I am trying load and running on R the  following function

// psi.cpp -- psi function for real arguments.

//      Algorithms and coefficient values from "Computation of Special

//      Functions", Zhang and Jin, John Wiley and Sons, 1996.

//

//  (C) 2003, C. Bond. All rights reserved.

//

//  Returns psi function for real argument 'x'.

//  NOTE: Returns 1e308 for argument 0 or a negative integer.

//

#include <iostream.h> // or <stdio.h>?

#include <math.h>

#define el 0.5772156649015329



double psi(double x)

{

    double s,ps,xa,x2;

    int n,k;

    static double a[] = {

        -0.8333333333333e-01,

         0.83333333333333333e-02,

        -0.39682539682539683e-02,

         0.41666666666666667e-02,

        -0.75757575757575758e-02,

         0.21092796092796093e-01,

        -0.83333333333333333e-01,

         0.4432598039215686};



    xa = fabs(x);

    s = 0.0;

    if ((x == (int)x) && (x <= 0.0)) {

        ps = 1e308;

        return ps;

    }

    if (xa == (int)xa) {

        n = xa;

        for (k=1;k<n;k++) {

            s += 1.0/k;

        }

        ps =  s-el;

    }

    else if ((xa+0.5) == ((int)(xa+0.5))) {

        n = xa-0.5;

        for (k=1;k<=n;k++) {

            s += 1.0/(2.0*k-1.0);

        }

        ps = 2.0*s-el-1.386294361119891;

    }

    else {

        if (xa < 10.0) {

            n = 10-(int)xa;

            for (k=0;k<n;k++) {

                s += 1.0/(xa+k);

            }

            xa += n;

        }

        x2 = 1.0/(xa*xa);

        ps = log(xa)-0.5/xa+x2*(((((((a[7]*x2+a[6])*x2+a[5])*x2+

            a[4])*x2+a[3])*x2+a[2])*x2+a[1])*x2+a[0]);

        ps -= s;

    }

    if (x < 0.0)

        ps = ps - M_PI*cos(M_PI*x)/sin(M_PI*x)-1.0/x;

        return ps;

}


However, when applicated the codes
>digamma(-0.9)
[1] -9.312644  OK!

But when
> dyn.load("psi.so")
> out<-.C("psi", as.double(-0.9))
Erro en .C("psi", as.double(-0.9)) : C symbol name "psi" not in load table

> out
Error: objeto "out" no encontrado

More information on OS:
> version
               _
platform       i486-pc-linux-gnu
arch           i486
os             linux-gnu
system         i486, linux-gnu
status
major          2
minor          4.1
year           2006
month          12
day            18
svn rev        40228
language       R
version.string R version 2.4.1 (2006-12-18)



Many thanks for any insight or comments.

Bernardo Lagos A.