Three different types of user defined functions (UDF) are used in AddiDict:

• The Particle Motion UDF, to change the equations that describe the particle motion.
• The Collision UDF, to define collision models in addition to the in-built models (Caught on First Touch, Sieving, Hamaker, and Random).
• The User Data UDF can be used in combination with one of the other UDF types. It allows to attach additional data to a particle, which can be used and modified during the simulation.

During the first startup, GeoDict copies a number of sample UDFs into the user’s directory at:

• Linux: /home/username/.geodict2025/UDF/
• Windows: C:\Users\username\GeoDict2025\UDF\

These files contain the Particle Motion UDFs:

• ParticleMotionUDF-Standard.cpp
• ParticleMotionUDF-Gravity.cpp
• ParticleMotionUDF-GravityPlusBuoyancy.cpp

These files contain the Collision UDFs:

• CollisionUDF-Count.cpp
• CollisionUDF-Hamaker.cpp

The files UDFUserData.h and UDFUserData.cpp can be used to define and initialize a user defined struct. GeoDict does not compile the source code (*.cpp) automatically. Therefore, the user has to compile the UDF before using it in GeoDict. Here, only the usage of Particle Motion UDFs is described, since they are commonly used in AddiDict. Details about using Collision UDFs and User Data UDFs can be found in the FilterDict user guide.