在並行計算中經常需要調用scalapck(並行化的lapack)函數庫裏面的函數進行編程，這裏簡單介紹在C語言如何調用scalapck中的矩陣向量乘的函數。

註意：scalapack中的函數是用fortran寫的，矩陣是按列進行存儲的。

scalapack的鏈接需要用到blas，因此確保本機上安裝好了blas、gfortran

下面是一個矩陣向量乘法的例子(為了簡單計算，該程序中設定進程數為4):

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include "mpi.h"
#define
 
 AA(i,j) AA[(i)*M+(j)]

int main(int argc, char **argv) 
{
   int i, j, k;
/************  MPI ***************************/
   int myrank_mpi, nprocs_mpi;
   MPI_Init( &argc, &argv);
   MPI_Comm_rank(MPI_COMM_WORLD, &myrank_mpi);
   MPI_Comm_size(MPI_COMM_WORLD, &nprocs_mpi);
/************  BLACS **************************
 
*/
   int ictxt, nprow, npcol, myrow, mycol,nb;
   int info,itemp;
   int ZERO=0,ONE=1;
   nprow = 2; 
   npcol = 2; 
   nb = 1;
   Cblacs_pinfo( &myrank_mpi, &nprocs_mpi ) ;
   Cblacs_get( -1, 0, &ictxt );
   Cblacs_gridinit( &ictxt, "Row", nprow, npcol );
   Cblacs_gridinfo( ictxt, &nprow, &npcol, &myrow, &mycol );
   
 
int M = 4;

   int descA[9],descx[9],descy[9];
   int mA = numroc_( &M, &nb, &myrow, &ZERO, &nprow );
   int nA = numroc_( &M, &nb, &mycol, &ZERO, &npcol );
   int nx = numroc_( &M, &nb, &myrow, &ZERO, &nprow );
   int my = numroc_( &M, &nb, &myrow, &ZERO, &nprow );
   descinit_(descA, &M, &M, &nb,  &nb,  &ZERO, &ZERO, &ictxt, &mA,  &info);
   descinit_(descx, &M, &ONE,  &nb, &ONE,  &ZERO, &ZERO, &ictxt, &nx, &info);
   descinit_(descy, &M, &ONE,   &nb, &ONE,  &ZERO, &ZERO, &ictxt, &my, &info);

   double *x = (double*) malloc(nx*sizeof(double));
   double *y = (double*) calloc(my,sizeof(double));
   double *A = (double*) malloc(mA*nA*sizeof(double));
   int sat,sut;
   for(i=0;i<mA;i++)
      for(j=0;j<nA;j++)
        A[j*mA+i]=1.0;
   for(i=0;i<nx;i++)
       x[i] = 1.0;
   double alpha = 1.0; double beta = 0.0;
   pdgemv_("N", &M, &M, &alpha, A, &ONE, &ONE, descA, x, &ONE, &ONE,descx, &ONE, &beta, y, &ONE, &ONE, descy, &ONE);

   for(i=0;i<my;i++)
   printf("rank=%d ,%f \n", myrank_mpi,y[i]);
   MPI_Finalize();
   return 0;
}    

編譯生成可執行文件:

mpicc -o pdgemv pdgemv.c -L/opt/scalapack/scalapck-2.0.2/ -lscalapack -lblas -lgfortran

運行：

mpirun -np 4 ./pdgemv

Linux系統下C語言如何調用scalapack中的函數