feat: Add fatras python example + test (#1030)

This PR adds an example python script to run Fatras and write outputs to various formats. It also adds a test to check this behavior.

Examples/Python/tests/test_examples.py

@@ -61,6 +61,40 @@ def assert_entries(root_file, tree_name, exp):
     assert rf.Get(tree_name).GetEntries() == exp, f"{root_file}:{tree_name}"
 
 
+def test_fatras(trk_geo, tmp_path, field):
+    from fatras import runFatras
+
+    csv = tmp_path / "csv"
+    csv.mkdir()
+
+    nevents = 10
+
+    root_files = [
+        ("fatras_particles_final.root", "particles", nevents),
+        ("fatras_particles_initial.root", "particles", nevents),
+        ("hits.root", "hits", 115),
+    ]
+
+    assert len(list(csv.iterdir())) == 0
+    for rf, _, _ in root_files:
+        assert not (tmp_path / rf).exists()
+
+    seq = Sequencer(events=nevents)
+    runFatras(trk_geo, field, str(tmp_path), s=seq).run()
+
+    del seq
+
+    assert_csv_output(csv, "particles_final")
+    assert_csv_output(csv, "particles_initial")
+    assert_csv_output(csv, "hits")
+    for f, tn, exp_entries in root_files:
+        rfp = tmp_path / f
+        assert rfp.exists()
+        assert rfp.stat().st_size > 2 ** 10 * 10
+
+        assert_entries(rfp, tn, exp_entries)
+
+
 def test_propagation(tmp_path, trk_geo, field, seq):
     from propagation import runPropagation
 

Examples/Scripts/Python/fatras.py

@@ -0,0 +1,127 @@
+#!/usr/bin/env python3
+import os
+
+import acts
+import acts.examples
+
+u = acts.UnitConstants
+
+
+def runFatras(trackingGeometry, field, outputDir, s: acts.examples.Sequencer = None):
+
+    # Preliminaries
+    rnd = acts.examples.RandomNumbers()
+
+    # Input
+    vtxGen = acts.examples.GaussianVertexGenerator()
+    vtxGen.stddev = acts.Vector4(0, 0, 0, 0)
+
+    ptclGen = acts.examples.ParametricParticleGenerator(
+        p=(1 * u.GeV, 10 * u.GeV), eta=(-2, 2)
+    )
+
+    g = acts.examples.EventGenerator.Generator()
+    g.multiplicity = acts.examples.FixedMultiplicityGenerator()
+    g.vertex = vtxGen
+    g.particles = ptclGen
+
+    evGen = acts.examples.EventGenerator(
+        level=acts.logging.INFO,
+        generators=[g],
+        outputParticles="particles_input",
+        randomNumbers=rnd,
+    )
+
+    # Selector
+    selector = acts.examples.ParticleSelector(
+        level=acts.logging.INFO,
+        inputParticles=evGen.config.outputParticles,
+        outputParticles="particles_selected",
+    )
+
+    # Simulation
+    alg = acts.examples.FatrasSimulation(
+        level=acts.logging.INFO,
+        inputParticles=selector.config.outputParticles,
+        outputParticlesInitial="particles_initial",
+        outputParticlesFinal="particles_final",
+        outputSimHits="simhits",
+        randomNumbers=rnd,
+        trackingGeometry=trackingGeometry,
+        magneticField=field,
+        generateHitsOnSensitive=True,
+    )
+
+    # Sequencer
+    s = s or acts.examples.Sequencer(
+        events=100, numThreads=-1, logLevel=acts.logging.INFO
+    )
+
+    s.addReader(evGen)
+    s.addAlgorithm(selector)
+    s.addAlgorithm(alg)
+
+    # Output
+    s.addWriter(
+        acts.examples.CsvParticleWriter(
+            level=acts.logging.INFO,
+            outputDir=outputDir + "/csv",
+            inputParticles="particles_final",
+            outputStem="particles_final",
+        )
+    )
+
+    s.addWriter(
+        acts.examples.RootParticleWriter(
+            level=acts.logging.INFO,
+            inputParticles="particles_final",
+            filePath=outputDir + "/fatras_particles_final.root",
+        )
+    )
+
+    s.addWriter(
+        acts.examples.CsvParticleWriter(
+            level=acts.logging.INFO,
+            outputDir=outputDir + "/csv",
+            inputParticles="particles_initial",
+            outputStem="particles_initial",
+        )
+    )
+
+    s.addWriter(
+        acts.examples.RootParticleWriter(
+            level=acts.logging.INFO,
+            inputParticles="particles_initial",
+            filePath=outputDir + "/fatras_particles_initial.root",
+        )
+    )
+
+    s.addWriter(
+        acts.examples.CsvSimHitWriter(
+            level=acts.logging.INFO,
+            inputSimHits=alg.config.outputSimHits,
+            outputDir=outputDir + "/csv",
+            outputStem="hits",
+        )
+    )
+
+    s.addWriter(
+        acts.examples.RootSimHitWriter(
+            level=acts.logging.INFO,
+            inputSimHits=alg.config.outputSimHits,
+            filePath=outputDir + "/hits.root",
+        )
+    )
+
+    return s
+
+
+if "__main__" == __name__:
+
+    gdc = acts.examples.GenericDetector.Config()
+    detector = acts.examples.GenericDetector()
+    trackingGeometry, contextDecorators = detector.finalize(gdc, None)
+
+    field = acts.ConstantBField(acts.Vector3(0, 0, 2 * u.T))
+
+    runFatras(trackingGeometry, field, os.getcwd()).run()