Pythia runs are five times slower with MadDM

Are you using the same version of pythia8 (and potentially lhapdf?)?

Cheers,

Olivier

Hi Olivier,

As for Pythia, yes I am using exactly the same version which is the 8.306.

Instead, as for lhapdf, I not sure. When I enter in MadDM it says:
"set lhapdf to /Users/mattiadimauro/Dropbox/MadDM/MG5_aMC_v2_9_9/HEPTools/lhapdf6/bin/lhapdf-config
set ninja to /Users/mattiadimauro/Dropbox/MadDM/MG5_aMC_v2_9_9/HEPTools/lib
None does not seem to correspond to a valid lhapdf-config executable.
Please set the 'lhapdf' variable to the (absolute) /PATH/TO/lhapdf-config (including lhapdf-config).
Note that you can still compile and run aMC@NLO with the built-in PDFs"
So there seems to be some problem with importing the lhapdf package.
I have lhapdf installed through MadDM in the folder:
MG5_aMC_v2_9_9/HEPTools/lhapdf6.
I tried to do:
"set lhapdf set lhapdf /Users/mattiadimauro/Dropbox/MadDM/MG5_aMC_v2_9_9/HEPTools/lhapdf6/bin/lhapdf-config" and it says:
"MadDM>set lhapdf /Users/mattiadimauro/Dropbox/MadDM/MG5_aMC_v2_9_9/HEPTools/lhapdf6/bin/lhapdf-config
set lhapdf to /Users/mattiadimauro/Dropbox/MadDM/MG5_aMC_v2_9_9/HEPTools/lhapdf6/bin/lhapdf-config
save options lhapdf
save configuration file to /Users/mattiadimauro/Dropbox/MadDM/MG5_aMC_v2_9_9/input/mg5_configuration.txt"
But then anytime I enter in MadDM there is still the message:
"None does not seem to correspond to a valid lhapdf-config executable.
Please set the 'lhapdf' variable to the (absolute) /PATH/TO/lhapdf-config (including lhapdf-config)."
Could this be the origin of the issue?

Best

Mattia

Hi Olivier,

(I used Pythia 8.306 with MadGraph LTS for the following tests)

I have an update on this question. I have run the main101 of MadDM using the same model and same LHEF file in few ways:
1. using Pythia compiled from MadGraph;
2. using an independent version of Pythia compiled by myself with the default flags.

In the case 2. I record an improvement of 5 in speed (from 24 s to 3 s for 10k events).

I then inspected the compilation flags that MadGraph uses, from the pythia8_install.log with respect to the ones used when compiling Pythia myself.
I found that in the latter case, there is also `-O2` which should optimize the code.
At this point, I used the installPYTHIA8.sh script in HEPToolsInstaller folder to compile a version of Pythia like MadGraph would do (I passed the same options that MadGraph also passes) and I have added the flag `-O2` to CXX_COMMON.

I repeated the test 1. and I recorded a time of 5 s.
In conclusion, I think that if we could add the optimization flag to the Pythia compilation happening in MadGraph, we could record a performance improvement in Pythia runs.

However, I ignore if there is a particular reason for which the optimization flag for the Pythia compilation has not been added.

Cheers.
--
Daniele

PS:
I verified that in the HEPToolsInstaller.py, the `-O2` flag is not passed for Pythia (like it happens for ninja, for e.g.).
Moreover, I inspected the configure script of pythia8 and I found that if --cxx-common is passed as a configuration option, and no debug is selected (as MadGraph is doing), then the following construct that sets CXX_COMMON is skipped (lines :
```
if [ -z "$CXX_COMMON" ]; then
    CXX_COMMON="${ENABLE_DEBUG}${ENABLE_64BIT}"
    CXX_COMMON="${CXX_COMMON}-std=c++11 -pedantic -W -Wall -Wshadow -fPIC"; fi
```
it contains the variable ENABLE_DEBUG, which is set at line 304:
```
[ "$ENABLE_DEBUG_SET" = true ] && ENABLE_DEBUG="-g " || ENABLE_DEBUG="-O2 "
```
So ENABLE_DEBUG contains the optimization flag, which is added to CXX_COMMON only in the case this is not passed from outside.
This demonstrates why the optimization is active if Pythia is compiled with no flags (like I did in the test 2.)
The slight changes in the configure script of Pythia in version 8.308 (latest version) do not affect what I wrote.

Should be fixed in the latest version of HEPTOOLSInstaller.