Cypress CSC-1200T Betriebsanweisung PDF herunterladen (Seite 54)

54 Cray T3E User’s Guide

6.3 Calling Fortran from C

Sometimes you need to call Fortran routines from C programs. In the

following, we calculate a matrix product using the routine SGEMM from

the Libsci library:

#include <stdio.h>

#include <fortran.h>

#define DGEMM SGEMM

#define l 450

#define m 500

#define n 550

main()

{

double a[n][l], b[l][m], ct[m][n];

int ll, mm, nn, i, j, k;

double alpha = 1.0;

double beta = 0.0;

void DGEMM();

char *transposed = "t";

_fcd ftran;

/* Initialize */

for(i=0;i<n;i++)

for(j=0;j<l;j++)

a[i][j] = i-j+2;

for(i=0;i<l;i++)

for(j=0;j<m;j++)

b[i][j] = 1/(double)(i+2*j+2);

ftran = _cptofcd(transposed, strlen(transposed));

ll=l;mm=m;nn=n;

DGEMM(ftran, ftran, &nn, &mm, &ll, &alpha, a, &ll,

b, &mm, &beta, ct, &nn);

printf("%.6f\n", ct[10][10]);

exit(0);

}

Note that on the T3E, the SGEMM routine performs the calculation using

64-bit real numbers, corresponding to the double type in C. Before mak-

ing the Libsci call, we need to convert the C strings into Fortran strings.

This is done with the function _cptofcd. We also use the type _fcd

deﬁned in the header ﬁle fortran.h.

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Cypress CSC-1200T Betriebsanweisung Seite 54