Using LAPACK in LINUX based environment with C++

Question

this is my very first question :)

I guess it is not qualified as should as be but this is what I am working on and It would be very nice to get someones opinion on this.

I am currently working on using LAPACK in a Linux based environment and I am very confused with it. I am trying to use C++ but I can code with Python also. First of all, I don't have root in the HPC, I am connecting to the school’s server, so I am not flexible as much as I need in terms of software.

I can write and compile any other C++ codes that require very basic includes such as string and so on. However, I could not find a way to be able to include necessary things or links with the LAPACK project.

For example: Understanding LAPACK calls in C++ with a simple example

//LAPACK test code
//compile with: g++ main.cpp -llapack -lblas -o testprog

#include <iostream>
#include <vector>

using namespace std;

extern "C" void dgetrf_(int* dim1, int* dim2, double* a, int* lda, int* ipiv, int* info);
extern "C" void dgetrs_(char *TRANS, int *N, int *NRHS, double *A, int *LDA, int *IPIV, double *B, int *LDB, int *INFO );


int main()
{
   char trans = 'N';
   int dim = 2;
   int nrhs = 1;
   int LDA = dim;
   int LDB = dim;
   int info;

   vector<double> a, b;

   a.push_back(1);
   a.push_back(1);
   a.push_back(1);
   a.push_back(-1);

   b.push_back(2);
   b.push_back(0);

   int ipiv[3];

   dgetrf_(&dim, &dim, &*a.begin(), &LDA, ipiv, &info);
   dgetrs_(&trans, &dim, &nrhs, & *a.begin(), &LDA, ipiv, & *b.begin(), &LDB, &info);


   std::cout << "solution is:";
   std::cout << "[" << b[0] << ", " << b[1] << ", " << "]" << std::endl;
   std::cout << "Info = " << info << std::endl;

   return(0);
}

There is this argument that is really close to what I am trying to do, solve a basic system with LAPACK. When I tried to use that code here is the error that I am facing with:

g++ main.cpp -llapack -lblas -o testprog
/cta/capps/lapack/3.9.0/lib/../lib/liblapack.a(xerbla.f.o): In function `xerbla_':
xerbla.f:(.text+0x49): undefined reference to `_gfortran_st_write'
xerbla.f:(.text+0x54): undefined reference to `_gfortran_string_len_trim'
xerbla.f:(.text+0x69): undefined reference to `_gfortran_transfer_character_write'
xerbla.f:(.text+0x79): undefined reference to `_gfortran_transfer_integer_write'
xerbla.f:(.text+0x81): undefined reference to `_gfortran_st_write_done'
xerbla.f:(.text+0x8a): undefined reference to `_gfortran_stop_string'
collect2: error: ld returned 1 exit status

I really need some advice or source to understand the logic behind the LAPACK and linking it with C++.

Thanks in advance...

Welcome. Please try this post https://stackoverflow.com/questions/16710047/usr-bin-ld-cannot-find-lnameofthelibrary — Z E Nir, Apr 07 '20 at 19:39

score 1 · Answer 1 · answered Apr 07 '20 at 20:13

LAPACK is written in fortran. The linking error indicates that your version of LAPACK was compiled with gfortran, which has a helper (runtime) library. To expand on other comments, you need to link this runtime library to provide the missing functions. Try adding -lgfortran to your link line (after -lblas), but before the -o. Hopefully that helps.

Using LAPACK in LINUX based environment with C++

1 Answers1