How to add BLAS_LIB in my Qt project? - c++

Question

I am using BLAS_LIB in my project to perform matrix multiplication. This is my CMakelist.txt. It was missing the path to BLAS_LIB and BLAS_INCLUDE file. I think it is the reason for the below error. If is the correct reason, please help me to fix it?
This is my CMakeList
cmake_minimum_required(VERSION 2.6)
project(testconv)
if(UNIX)
SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -std=gnu++0x")
endif()
add_executable(testconv main.cpp)
install(TARGETS testconv RUNTIME DESTINATION bin)
This is the error
/home/projects/TestConv/main.cpp:24: undefined reference to `cblas_dgemm'
This is my cpp file
#include <iostream>
#include <random>
#include <cblas.h>
int main ( int argc, char* argv[] ) {
//Random numbers
std::mt19937_64 rnd;
std::uniform_real_distribution<double> doubleDist(0, 1);
//Create Arrays that represent the matrices A,B,C
const int n = 20;
double* A = new double[n*n];
double* B = new double[n*n];
double* C = new double[n*n];
//Fill A and B with random numbers
for(uint i =0; i <n; i++){
for(uint j=0; j<n; j++){
A[i*n+j] = doubleDist(rnd);
B[i*n+j] = doubleDist(rnd);
}
}
//Calculate A*B=C
cblas_dgemm(CblasRowMajor, CblasNoTrans, CblasNoTrans, n, n, n, 1.0, A, n, B, n, 0.0, C, n);
//Clean up
delete[] A;
delete[] B;
delete[] C;
return 0;
}

Answer 1

Yes, you're completely forgetting to include the BLAS library.
For your CMake version CMake includes a FindBLAS.cmake file, which will not work in your case.
You will need FindCBLAS.cmake that correctly will find the C interface to BLAS as done in other open source projects.
You can grab for example the following https://github.com/Eyescale/CMake/blob/master/FindCBLAS.cmake.
First of all you will need to create a directory called cmake in your project root directory (not in the build directory!!!), then copy that file I just mentioned (FindCBLAS.cmake).
You will need to modify your CMakeLists.txt in the following:
cmake_minimum_required(VERSION 2.6)
project(testconv)
set(CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/cmake)
find_package(CBLAS REQUIRED)
include_directories(${CBLAS_INCLUDE_DIR})
if(UNIX)
SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -std=gnu++0x")
endif()
add_executable(testconv main.cpp)
target_link_libraries(testconv ${CBLAS_LIBRARIES})
install(TARGETS testconv RUNTIME DESTINATION bin)
Try that. It can be improved, but should get you started.