This README is about the extension of G4HepEm with AD capabilities. See README_ORIGINAL.md for information about G4HepEm.

Differentiated G4HepEm

G4HepEm is a compact, self-contained toolkit for electromagnetic shower simulation. This repository contains a version of G4HepEm that has been extended with operator-overloading algorithmic differentiation (AD) capabilities using CoDiPack CoDiPack, making it possible to

• propagate dot values through G4HepEm functionalities with forward-mode AD, and
• record G4HepEm calculations on a "tape" to implement operator-overloading reverse-mode AD.

This differentiated version of G4HepEm is used by a differentiated version of HepEmshow to compute derivatives in a simple calorimetry setup.

Building from source

A version of G4HepEm without any AD capabilities can be built as usual: Download the code into some directory, enter the directory, checkout the with_codipack branch, and run

mkdir build
cd build
cmake ../ -DG4HepEm_GEANT4_BUILD=OFF -DCMAKE_INSTALL_PREFIX=$PWD/../install -DCMAKE_BUILD_TYPE=Release
make
make install

To create a forward-mode or reverse-mode AD build, supply -DCODI_FORWARD=yes or -DCODI_REVERSE=yes to the cmake call, respectively. Most likely, you also have to download the AD tool CoDiPack and specify its path to cmake via -DCoDiPack_DIR=/path/to/CoDiPack/cmake.

If you want to make non-AD and AD builds at the same time, consider using directory names build_no/build_ad and $PWD/../install_no/$PWD/../install_ad instead of build and $PWD/../install in the above build commands.

License Hints

G4HepEm has been released under the Apache-2.0 license. Please note that CoDiPack has been released under the GNU General Public License (GPL) version 3, which also applies to the combined work.