I use the ubuntu 9.04 jaunty jackalope along with other open source C++ libraries. Recently I discovered the fftw-3.2.2 libraries, but trying linking it is harder then I thought. Basically, I have to link these libraries -lfftw3 -lm but I do not know how ? Here is my CMakeLists.txt: PROJECT (ransac) cmake_minimum_required(VERSION 2.6) FIND_PACKAGE(VTK REQUIRED) IF(NOT VTK_USE_RENDERING) MESSAGE(FATAL_ERROR "Example ${PROJECT_NAME} requires VTK_USE_RENDERING.") ENDIF(NOT VTK_USE_RENDERING) INCLUDE(${VTK_USE_FILE}) SET(CMAKE_CXX_FLAGS "-Wall -Wno-deprecated") SET(CMAKE_BUILD_TYPE Debug) INCLUDE_DIRECTORIES (../common/levmar) LINK_DIRECTORIES (../../common/levmar) INCLUDE_DIRECTORIES (~/local/DIR/include) INCLUDE_DIRECTORIES (../common/ann/include) INCLUDE_DIRECTORIES (../common/ann/lib) LINK_DIRECTORIES (../../common/ann/lib) INCLUDE_DIRECTORIES (../common/fftw-3.2.2/.libs) LINK_DIRECTORIES (../../common/fftw-3.2.2/.libs) ADD_EXECUTABLE (fftw-test fftw-test.cc ../common/StringTokenizer.cc ../common/CommonANNRoutines.cc ../common/CommonVTKRoutines.cc ../common/CommonIORoutines.cc ../common/Common3DGeomRoutines.cc ../common/CommonTerminalRoutines.cc ../common/ANN-VTK.cc ../common/VTKShapes.cc ../common/CommonPrintRoutines.cc) TARGET_LINK_LIBRARIES (fftw-test vtkCommon vtkRendering vtkWidgets vtkHybrid vtkGraphics ANN lapack levmar) The section of code from fftw-test.cc is: #include "../common/fftw-3.2.2/api/fftw3.h" ... // points is an <ANNpointArray> with a number of <header.nr_points> 3D points // int p = 0; double *in = (double *) malloc (sizeof(double) * header.nr_points * 3); // add the the points' coordinates in row major order // // that means the X values first, then the Y values and at last the Z values // for ( int d = 0 ; d < 2; d++ ) for ( int idx = 0 ; idx < header.nr_points; idx++ ) { in [p] = points[idx][d]; p++; } int rank = 3; fftw_complex *out; unsigned flags; // and here is the problem // fftw_plan forward = fftw_plan_dft_r2c (rank, (const int*) (3 * header.nr_points), in, out, flags); fftw_execute (forward); Finally my bash output is: goron@lucian:~/work/ransac/build$ make fftw-test -- Configuring done -- Generating done -- Build files have been written to: /home/goron/work/ransac/build [ 10%] Building CXX object CMakeFiles/fftw-test.dir/fftw-test.cc.o [ 20%] Building CXX object CMakeFiles/fftw-test.dir/home/goron/work/common/StringTokenizer.cc.o [ 30%] Building CXX object CMakeFiles/fftw-test.dir/home/goron/work/common/CommonANNRoutines.cc.o [ 40%] Building CXX object CMakeFiles/fftw-test.dir/home/goron/work/common/CommonVTKRoutines.cc.o [ 50%] Building CXX object CMakeFiles/fftw-test.dir/home/goron/work/common/CommonIORoutines.cc.o [ 60%] Building CXX object CMakeFiles/fftw-test.dir/home/goron/work/common/Common3DGeomRoutines.cc.o [ 70%] Building CXX object CMakeFiles/fftw-test.dir/home/goron/work/common/CommonTerminalRoutines.cc.o [ 80%] Building CXX object CMakeFiles/fftw-test.dir/home/goron/work/common/ANN-VTK.cc.o [ 90%] Building CXX object CMakeFiles/fftw-test.dir/home/goron/work/common/VTKShapes.cc.o [100%] Building CXX object CMakeFiles/fftw-test.dir/home/goron/work/common/CommonPrintRoutines.cc.o Linking CXX executable fftw-test CMakeFiles/fftw-test.dir/fftw-test.cc.o: In function `main': fftw-test.cc:(.text+0x666): undefined reference to `fftw_plan_dft_r2c' fftw-test.cc:(.text+0x674): undefined reference to `fftw_execute' collect2: ld returned 1 exit status make[3]: *** [fftw-test] Error 1 make[2]: *** [CMakeFiles/fftw-test.dir/all] Error 2 make[1]: *** [CMakeFiles/fftw-test.dir/rule] Error 2 make: *** [fftw-test] Error 2 goron@lucian:~/work/ransac/build$ Has somebody encountered this problem before ? Thank you in advance.