How to link Lapack?

[mdelmar]

Hi!

I have just installed Lapack and Blas from Synaptic on Ubuntu 10.04. I'm trying to compile this simple programm:

Code: Select all

#include <stdio.h>
#include <clapack.h>
#include <cblas.h>


void sgesv( int* n, int* nrhs, float* a, int* lda, int* ipiv, float* b, int* ldb, int* info );

int main()
{
               
int uno = 1;
int tres = 3;

float A []={
2, 1, 1,
3, -1, 1,
0, 2, 3};

float x[]= {0, 0, 0};

float b [] = {1, 0, 3};

int ipiv[3];
int info;
int i;

sgesv (&tres, &uno, A, &tres, ipiv, b, &tres, &info);

for (i=0; i<3; ++i)  printf("%f\n", x[i]);

return 0;

}

But I get the following error: "undefinded reference to 'sgesv' " when I type "gcc lap.c -o lap -llapack -lblas"
I wrote another program that just uses BLAS and compiles fine with "gcc prueba.c -o prueba -lblas". However, this program using the lapack routine returns an error. Have I missed anything? What am I doing wrong?

Thanks in advance

[admin]

Hi,
You got a Fortran Mangling Problem.
Adding an underscore to the name of the routine should do the trick. (it can be different depending on your system)

Here is your code that works.

Code: Select all

#include <stdio.h>
void sgesv_( int* n, int* nrhs, float* a, int* lda, int* ipiv, float* b, int* ldb, int* info );

int main()
{
int uno = 1;
int tres = 3;

float A []={
2, 1, 1,
3, -1, 1,
0, 2, 3};

float x[]= {0, 0, 0};

float b [] = {1, 0, 3};

int ipiv[3];
int info;
int i;

sgesv_ (&tres, &uno, A, &tres, ipiv, b, &tres, &info);
printf("INFO SGESV=%d\n", info);
for (i=0; i<3; ++i)  printf("%f\n", b[i]);

return 0;
}

and here is the way to compile and link:

Code: Select all

gcc -c lap.c
gfortran lap.o -o lap -llapack -lblas

Best would be to use the Standard C language APIs for LAPACK.
It is available here: http://www.netlib.org/lapack/#_standard ... for_lapack
Your program will look like this:

Code: Select all

#include <stdio.h>
#include "lapacke.h"

int main()
{
float A []={
2, 1, 1,
3, -1, 1,
0, 2, 3};

float x[]= {0, 0, 0};

float b [] = {1, 0, 3};

int ipiv[3];
int info;
int i;

info = LAPACKE_sgesv (LAPACK_COL_MAJOR, 3, 1, A, 3, ipiv, b, 3);
printf("INFO SGESV=%d\n", info);
for (i=0; i<3; ++i)  printf("%f\n", b[i]);

return 0;
}

and to compile and link

Code: Select all

gcc -c newlap.c
gfortran newlap.o -o newlap -llapacke -llapack -lblas

Julie

[mdelmar]

Wow, Julie, thank you for yor help. I totally forgot the underscore because I'm using a guide for Fortran.

[venkatesh]

Hi,
I am linux newbie....

I have installed Lapack 3.4 version and I tried to use the example program...compiled and linked using

gcc -c newlap.c
gfortran newlap.o -o newlap -llapacke -llapack -lblas

It gives me an error

"/usr/bin/ld: cannot find -llapacke"

Please help me......

[venkatesh]

Hi ,

I am new to linux,

I just blindly followed the steps for instaling lapack 3.4 and also tried to test it using your example program it gave me the following error

"cannot find llapacke"

I used the following commands
gcc -c newlap.c
gfortran newlap.o -o newlap -llapacke -llapack -lblas

Please help me.....

[selvvy]

solved my problem, thanks