How do you correctly define the dependencies to FFTW in a cmake file?

Question

I want to use fftw in my c++ program. For this, I have installed petsc alongside the --download-fftw option, since I want to be using Petsc in the future as well. I simply downloaded the most recent stable version, ran ./configure with the respective options and then make -> sudo make install

The files are now located in /usr/local/petsc, which contain the following fftw files:

$ ls /usr/local/petsc/include/
...
fftw3-mpi.f03
fftw3-mpi.h
fftw3.f
fftw3.f03
fftw3.h
fftw3l-mpi.f03
fftw3l.f03
fftw3q.f03
... 

$ ls /usr/local/petsc/lib/
...
libfftw3.a
libfftw3.la
libfftw3.so
libfftw3.so.3
libfftw3.so.3.6.10
libfftw3_mpi.a
libfftw3_mpi.la
libfftw3_mpi.so
libfftw3_mpi.so.3
libfftw3_mpi.so.3.6.10
...

I then defined my CMakeLists.txt file for my project as following:

cmake_minimum_required(VERSION 3.0)
find_package(MPI REQUIRED)
add_executable(my_program my_program.cpp)

set(PETSC_DIR "/usr/local/petsc")
target_include_directories(my_program PUBLIC 
                           ${MPI_INCLUDE_PATH} 
                           ${PETSC_DIR}/include)
target_link_libraries(my_program PUBLIC 
                      ${MPI_LIBRARIES} 
                      ${PETSC_DIR}/lib)

In my_program, I simply call fftw_mpi_init():

#include <mpi.h>
#include <fftw3-mpi.h>
int main(){
  MPI_Init(NULL, NULL);
  fftw_mpi_init();
}

However, this setup returns the error message

undefined reference to `fftw_mpi_init'

I realized that fftw_mpi_init was not defined anywhere in my /usr/local/petsc directory:

Is this related to my c++ program not being able to find the fftw functions? What steps do I need to take if I want to use the fftw installation that I downloaded alongside petsc?

EDIT: I also tried adding the lines

find_package(PkgConfig REQUIRED)
pkg_search_module(FFTW REQUIRED fftw3 IMPORTED_TARGET)
include_directories(PkgConfig::FFTW)
link_libraries     (PkgConfig::FFTW)

to my CMakeLists.txt file as suggested here, but I am still getting the same error undefined reference to fftw_mpi_init'.

This is probably what you want: [https://stackoverflow.com/a/68220409/487892](https://stackoverflow.com/a/68220409/487892) — drescherjm, Mar 09 '23 at 12:43
@drescherjm thanks for the suggestion but unfortunately it didn't work for me, I updated my question accordingly. — Yes, Mar 09 '23 at 12:46

score 0 · Answer 1 · answered Mar 09 '23 at 13:14

The solution was to include ${PETSC_DIR}/lib/libfftw3_mpi.a (the file where fftw_mpi_init is defined) and -lfftw3 in my linker command:

...
target_link_libraries(my_program PUBLIC 
                      ${MPI_LIBRARIES} 
                      ${PETSC_DIR}/lib/libfftw3_mpi.a
                      -lfftw3)
...

How do you correctly define the dependencies to FFTW in a cmake file?

1 Answers1