libtorch (C++-only)
===================

The core of pytorch does not depend on Python. A
CMake-based build system compiles the C++ source code into a shared
object, libtorch.so.

Building libtorch
-----------------

You can use a python script/module located in tools package to build libtorch
::
   cd <pytorch_root>

   # Make a new folder to build in to avoid polluting the source directories
   mkdir build_libtorch && cd build_libtorch

   # You might need to export some required environment variables here.
   Normally setup.py sets good default env variables, but you'll have to do
   that manually.
   python ../tools/build_libtorch.py


Alternatively, you can call setup.py normally and then copy the built cpp libraries. This method may have side effects to your active Python installation.
::
   cd <pytorch_root>
   python setup.py build

   ls torch/lib/tmp_install # output is produced here
   ls torch/lib/tmp_install/lib/libtorch.so # of particular interest

To produce libtorch.a rather than libtorch.so, set the environment variable `BUILD_SHARED_LIBS=OFF`.

To use ninja rather than make, set `CMAKE_GENERATOR="-GNinja" CMAKE_INSTALL="ninja install"`.

Note that we are working on eliminating tools/build_pytorch_libs.sh in favor of a unified cmake build.