# PhD discussion Wed 19.10.2022

Present: ZW, OM, SR, RS + AV (10 minutes late - notes)

## Discussion of reweighting

ZW: many parameters in parallel rather than in sequence? 
OM: in some cases it may be better to sacrifice a bit of performance to keep flexibility
AV: would not change the event-level parallelism, especially on c++ it would be a profoiund reengineering
SR: anyway the number of events is large, we can parallelize at the level of events
RS: typically running thousands of events at least
AV: also for #events on GPU we might reduce that by also parallelizing on helicities
OM: correct, we still keep sum over helicities inside the reweighting

SR: Robert is doing also Pythia now, if MG goes faster, maybe Pythia become a bottleneck?
RS: will follow up, interesting question how much Pythia is consuming
AV: however reweighting only does MG, while Pythia PS/hadronization and Geant4 are not rerun
RS: correct, Pythia and Geant4 are spectators in reweighting

## Schools

ZW: Bertinoro was great, very varied programme from hardware to programming
ZW: second school was advanced C++ by SR et al, also great but more specific to C++ features only

ZW: now rewrote an LHE file parser in C++, it is around x5 faster than the Python version by Olivier
(x5 faster when it does not segfault, still a few issues to fix)
OM: this is used for reweighting but also elsewhere eg for final unweighting

## Lugano discussion (MLM and single precision)

OM: apart from using ME for reweighting, we are also working on integration in full madevent.
In Lugano we also worked on reducing overhead of madevent parts like MLM merging.
ZW moved one part from after the ME to before the ME calculation, this reduces memory and CPU significantly.
AV: need to cross check, but in juwels I seem to get a factor x10 (not x2!) for ggttggg...

OM/ZW: also worked on color algebra, moving it from double to single precision
Show a plot done by ZW (Fortran version pp process)

## Meeting with CMS

SR: will plan a meeting with Sapta in November
RS: please invite me
AV: please do it not before 14/11, 21/11 even better

## AOB

SR: next meeting? monthly enough or prefer biweekly?
ZW: maybe in one month from now, then biweekly (I am on holiday forst two weeks of november)
OM: how about Monday 14 at 1pm?