Tests

Material Budget LUT classes

To generate the LUT (at the moment for R<400, with layers above 270 cm not optimized) run

root -b -q O2/Detectors/Base/test/buildMatBudLUT.C+

The generation is quite time consuming (may take ~30 min).

It can be filled in parallel, one TGeoNavigator per thread, by passing a thread count as the 7th argument of buildMatBudLUT or by setting the environment variable:

export NTHREADS_MATBUD=16

The result does not depend on the number of threads. Scaling beyond a few threads needs ROOT >= v6-36-10-alice3, which removes the per-query thread-id lookup and the false sharing between the per-thread scratch buffers of TGeo shapes; with older ROOT the parallel path is still correct, just slower.

An alternative VecGeom geometry backend can be selected via the 8th argument ("ROOT" or "VECGEOM"), e.g.

root -b -q 'O2/Detectors/Base/test/buildMatBudLUT.C(60, -1, "matbud.root", "o2sim", "", 16, "VECGEOM")'

This requires O2 to have been built against the optional TGeo2VecGeom package (o2::base::GeometryManager::isVecGeomAvailable()); it is otherwise a build-time no-op that does not affect the default ROOT/TGeo path in any way.

The optimized LUT will be stored in the matbud.root file.

Load it as:

auto mbr = o2::base::MatLayerCylSet::loadFromFile("matbud.root");

To query mat. budget between 2 points use:

float xyz0[3] = {0.,0.,0.};
float xyz1[3] = {70.,80.,20.};
 
auto mb = mbl.getMatBudget(xyz0[0],xyz0[1],xyz0[2], xyz1[0],xyz1[1],xyz1[2]);
// alternatively, use MatCell getMatBudget(const math_utils::Point3D<float> &point0,const math_utils::Point3D<float> &point1) method
 
std::cout << "<rho>= " << mb.meanRho << " <x/X0>= " << mb.meanX2X0 << "\n";

Macro extractLUTLayers.C can be used to extract layers covering certain radius range to obtain more compact LUT.