5.3. Writing Gaudi Algorithms

Learning Objectives

This tutorial will teach you how to:

  • write an algorithm for FCCSW

  • interact with the cmake based build system

  • use other Gaudi components in the algorithms

5.3.1. Getting Started

Writing Gaudi components requires a bit of boilerplate code. Often it is easiest to start from existing files and modify them as needed. For this tutorial, there is a dedicated repository that contains an example. Start by cloning it locally:

git clone https://github.com/key4hep/k4-project-template

It contains a CMake configuration (as described in more detail in the previous tutorial) so it can be built with:

cd k4-project-template
mkdir build install
cd build
cmake .. -DCMAKE_INSTALL_PREFIX=../install
make -j 4

To run the algorithms contained in this repository, it is not necesary to run

make install

you can use the run script in the build directory, like:

./run fccrun ../K4TestFWCore/options/createExampleEventData.py

5.3.2. Exercise: Adding an Algorithm

The repository contains an EmptyAlg in K4TestFWCore/src/components.

  • As a first exercise, copy and modify this algorithm to print out the current event number.

  • Second step: If you used std::cout in the first step, try to use the gaudi logging service instead.

  • Third Step: Print out a string before the event number that should be configurable at runtime.

  • Finally: use the Gaudi Random Number Generator Service to approximate pi with a Monte Carlo Integration