Optimize Compile Time

Table of Contents

• Explicit Template Instantiation

Especially with increasing complexity of your project, compilation time of the CT can become long. However, there are some tricks to reduce compilation time

• make sure you compile in Release mode (catkin build -DCMAKE_BUILD_TYPE=RELEASE)
• use CLANG instead of gcc. See the build flags in the Installation Guide on how to use clang.
• use Explicit Template Instantiation

Explicit Template Instantiation

The Control Toolbox is a heavily templated library for best runtime performance. However, this means most code lives in header files and gets recompiled when any changes are made to the code. Needless to say, that this can become cumbersome after some time. However, there is a simple yet effective workaround: Explicit template instantiation. The idea is simple: You define the templates that are used before compilation and they get compiled into a library. In CT templates are:

Template Parameter	Description
STATE_DIM	The dimension of the system's system state
CONTROL_DIM	The dimension of the system's control input
SCALAR	The scalar type used (usually double)
POS_DIM	(optional) Dimension of the position vector for a symplectic system
VEL_DIM	(optional) Dimension of the velocity vector for a symplectic system

In case you are multiple systems of different dimensions, you can prespecify each of their dimensions.

To use explicit template instantiation follow these steps:

1. add your dimensions to ct/ct/config/explicit_templates.cfg . You can set POS_DIM and VEL_DIM to 0 if you are not using symplectic integrators.
2. rerun cmake and enable explicit template prespec: catkin build -DUSE_PRESPEC=true -DCMAKE_BUILD_TYPE=RELEASE –force-cmake
3. In your executable change the standard CT includes from their regular ones to the prespecified ones, e.g. change

   #include <ct/core/core.h>

   to

   #include <ct/core/core-prespec.h>

   Remember to do this for optcon and rbd as well.