marcelkunze / trackml

CodaLab trackml throughput phase

Below you can find a outline of how to reproduce my solution for the CodaLab trackML throughput competition. If you run into any trouble with the setup/code or have any questions please contact me at [email protected].

A multi threaded global tracking algorithm based on directed acyclic graphs and machine learning

The algorithm has been designed to make use of artificial neural networks for pattern recognition on the basis of spatial coordinates together with simple geometrical information such as directional cosines or a helix score calculation. Typical patterns to be investigated are hit pairs and triples that might seed candidate tracks. The training of the networks was accomplished by presentation of typically 5 million ground truth patterns over 500 epochs. The hit data are sorted into voxels organized in directed acyclic graphs (DAG) in order to allow for fast track propagation. In addition to the spatial hit data the DAGs hold information about the network model to apply, and a z vertex estimate derived from ground truth. As they combine the data with the corresponding methods the DAGs form a nice foundation to define tasks that can be run in parallel very efficiently in a multi threaded environment. There are two sets of graphs: One set covers detector slices along the z-axis, the other covers a phi/theta grid. Each set would work perfectly well by itself, but a clever combination of the two yields the best CodaLab score: The first set is used to seed the pair finder while the other drives the triple finder.

The path and track finding is based on inward/outward triple prolongation in combination with outlier density estimation as proposed by J.S. Wind in the Kaggle accuracy phase.

Running two threads the execution time is on average about 7 seconds per event at 93% accuracy in a docker environment, consuming 700 MB RAM.

ARCHIVE CONTENTS

*.cxx, *.h   : source files
Makefile     : build the model
paths, graph : DAGs
xmlp         : neural networks
doc          : documentation

HARDWARE

Ubuntu 18.04 LTS (256 GB SSD)
Intel NUC 7I7BNH (16 GB RAM)

SOFTWARE

• C++11 with STL
• Neural Network Objects or TMVA for training
• ROOT framework for training
• docker or singularity for testing and tuning

DATA SETUP

git clone https://github.com/marcelkunze/trackml.git
cd trackml
make eval

This builds a shared library libmodel.so and the eval C++ driver program that is good for evaluation purposes. For debugging and training purposes the tracker program should be built (requires the installation of the ROOT framework):

make tracker

DATA PROCESSING

Parameters and operational modes of the model are centrally defined in Parameters.h. The DATAPATH, the WORKPATH, and the TRAINPATH need to be adapted to fit the local installation. The model is run with

./eval 21001 10
./tracker 21001 10

where the arguments denote the event and the number of events to be processed in sequence, respectively. Processing is generally done in a container environment using a 50 events data set (training_000021450_000021499). The model can be tested by running it in a docker container using the CodaLab framework (Works w/o dependencies to external packages):

./rundocker.sh

This builds the C++ shared library and produces a zip-file of all files to be submitted to CodaLab. The model is executed in a python framework in the run directory.

The model works with singularity containers as well:

./runsingularity.sh

The scripts need to be modified to define the INPUT_DATA path to locate the data set.

MODEL BUILD

The DAGs reside in the graph (tiles) and paths (slices) directories, respectively. The training of the DAGs is performed by

./makeGraph [ event number mode phires theres ]

• event - event to process (default: 21001)
• number - number of events in sequence (default: 1)
• mode - 1 for tile graphs, 3 for slice graphs
• phires - phi resolution (default: 12)
• theres - theta resolution (default: 14)

Graph generation takes about half a minute for 25 events. There is a script to prepare a suiting set of graphs:

./generate.sh 25 12 14

where the argument denotes the number of events to use for training and the phi and theta resolution, respectively.

There are three neural networks for pattern recognition:

• XMLP1 for hit pair recognition (8-15-5-1 multilayer perceptron), good esp. in forward/backward detector region
• XMLP2 for hit pair recognition (9-15-5-1 multilayer perceptron), good esp. in central detector region
• XMLP3 for hit triple recognition (10-15-5-1 multilayer perceptron), good everywhere

The neural networks are trained with ntuples stored in ROOT files. These are produced if the flag TRAINFILE is set in the programs. The training has been performed with the NetworkTrainer of the Neural Network Objects by use of the corresponding training files, e.g.

NetworkTrainer train1.nno
NetworkTrainer train2.nno
NetworkTrainer train3.nno

The supervised training takes about half an hour for 500 epochs of 4-5 million patterns each (extracted from ca. 10 events). For each epoch the network file is stored in the Networks directory with a corresponding name. The network with the best validation performance is named NNO0000.TXMLP. After the training a suiting network has to be copied over to the xmlp directory respecting the names defined in Parameters.h.