mlpack/doc/user/compile.md

Compile an mlpack program

Once an mlpack application has been developed, it is easy to compile it into a standalone program. On this page, compilation is performed via the command-line on a standard Linux or OS X system; if this is not your environment, see also:

• Cross-compile to a Raspberry Pi 2
• Deploy mlpack on Windows

Simple command-line compilation

Assuming that mlpack and its dependencies are installed on the system, an mlpack program can be compiled just like any other C++ program:

g++ -std=c++17 -O3 -o mlpack_program mlpack_program.cpp -larmadillo -fopenmp

The command above uses gcc to compile the program mlpack_program.cpp in C++17 mode with optimizations, using OpenMP for parallelization. It is expected that mlpack_program.cpp has the int main() function defined.

For more complex applications that have multiple source files, it can often be easier to develop a simple Makefile.

The examples repository contains several standalone C++ projects, each of which have Makefiles. These can be adapted for any project, and are especially useful if any extra include directories or library directories need to be specified. (This might be the case if, for instance, mlpack or any dependencies are not installed to standard locations.)

• Example adaptable Makefile

A full list of compiler options to configure the build is beyond the scope of this simple documentation, but this simple list has a handful of commonly-used gcc/clang options.

Configuring mlpack with compile-time definitions

Several compilation options can control the behavior of an mlpack program. These can be specified directly on the command line, or at the top of the program (before including mlpack or Armadillo!).

Command-line option	Code option	Meaning
Speed and debugging.
-DNDEBUG	#define NDEBUG	Remove all debugging checks. This can result in slightly faster code, but with no error checking!
-DARMA_NO_DEBUG	#define ARMA_NO_DEBUG	Remove all Armadillo error checking. Warning: if there are errors in your code, you are more likely to get a segfault instead of an exception!
---------------------------	-------------------	---------------
Output.
-DMLPACK_COUT_STREAM=std::cout	#define MLPACK_COUT_STREAM std::cout	Set the default output stream. (Defaults to std::cout.)
-DMLPACK_CERR_STREAM=std::cerr	#define MLPACK_CERR_STREAM std::cerr	Set the default error stream. (Defaults to std::cerr.)
-DMLPACK_PRINT_INFO	#define MLPACK_PRINT_INFO	Print information messages ([INFO ]) during program execution.
-DMLPACK_PRINT_WARN	#define MLPACK_PRINT_WARN	Print warning messages ([WARN ]) during program execution.
-DMLPACK_SUPPRESS_FATAL	#define MLPACK_PRINT_FATAL	Do not print [FATAL] messages during program execution.
-DENS_PRINT_INFO	#define ENS_PRINT_INFO	Print informational messages from ensmallen optimizers.
-DENS_PRINT_WARN	#define ENS_PRINT_WARN	Print warning messages from ensmallen optimizers.
---------------------------	-------------------	---------------
Functionality.
-DMLPACK_ENABLE_ANN_SERIALIZATION	#define MLPACK_ENABLE_ANN_SERIALIZATION	Allow neural network layers to be serialized.
-DMLPACK_DISABLE_STB	#define MLPACK_DISABLE_STB	Disable STB-related image functionality.

Note: If your code serializes (saves or loads) mlpack neural networks, the MLPACK_ENABLE_ANN_SERIALIZATION option must be enabled. This option is not enabled by default because it can cause compilation time to increase significantly, but it is necessary for any code that serializes neural networks.

Linking without the Armadillo wrapper

Armadillo, by default, requires linking against the runtime library libarmadillo.so (or libarmadillo.dylib or armadillo.dll on non-Linux systems). This library is a convenience library that internally contains all of the symbols necessary from lower-level libraries (e.g. OpenBLAS, SuperLU, ARPACK, HDF5, and so on). When the wrapper library is used, linking against Armadillo means simply typing -larmadillo instead of linking against all of Armadillo's dependencies.

In some situations this is not preferable, and it is therefore possible via the ARMA_DONT_USE_WRAPPER macro to avoid the Armadillo runtime library and link directly against Armadillo's dependencies.

When the Armadillo wrapper library is not being used, a compilation command will need to be adjusted. For instance, the example of the previous section would need to be changed to:

g++ -DARMA_DONT_USE_WRAPPER -std=c++17 -O3 -o mlpack_program mlpack_program.cpp -lopenblas -fopenmp

Some notes on the command above:

• Here, ARMA_DONT_USE_WRAPPER is specified on the command line instead of in mlpack_program.cpp (or otherwise in the Armadillo configuration).

• OpenBLAS is used for BLAS/LAPACK support. But, other options include ACML, reference LAPACK/BLAS, Intel MKL, and so forth.

• In some programs, especially if sparse matrix support or HDF5 support is used, it may be necessary to link against other libraries (e.g. -lSuperLU -lhdf5, etc.). The precise set of libraries to link against depends on the code being used and the system configuration, but it should be easy enough to use any linker errors to figure out what libraries need to be linked against.

Using mlpack in another CMake project

For complex C++ projects, a build system like CMake may be in use. Adding mlpack as a dependency to a C++ project is straightforward. The following CMake code will require mlpack and its dependencies to be available:

# Find mlpack and its dependencies.
find_package(Armadillo REQUIRED)
find_package(cereal REQUIRED)
find_package(ensmallen REQUIRED)
find_package(mlpack REQUIRED)

include_directories("${ARMADILLO_INCLUDE_DIRS}" "${CEREAL_INCLUDE_DIR}"
    "${ENSMALLEN_INCLUDE_DIR}" "${MLPACK_INCLUDE_DIR}")

# Targets should link against ${ARMADILLO_LIBRARIES}.

If the relevant files are not available on the system to find those four packages, they can be downloaded from the models repository:

• models/CMake directory

The following files in that directory are necessary (and can be added to the CMake files for the project):

• ARMA_FindACML.cmake
• ARMA_FindACMLMP.cmake
• ARMA_FindARPACK.cmake
• ARMA_FindBLAS.cmake
• ARMA_FindCBLAS.cmake
• ARMA_FindCLAPACK.cmake
• ARMA_FindLAPACK.cmake
• ARMA_FindMKL.cmake
• ARMA_FindOpenBLAS.cmake
• FindArmadillo.cmake
• FindEnsmallen.cmake
• Findcereal.cmake
• Findmlpack.cmake