=== How do I implement my own renormalization/factorization scales in !MadEvent? ===

Since v.4.2.17, there is a new default dynamical scale choice in [http://cp3wks05.fynu.ucl.ac.be/cgi-bin/ViewVC/viewvc.cgi/MG_ME/Template/Cards/run_card.dat?view=markup run_card.dat] file: 

{{{
#*********************************************************************
# Renormalization and factorization scales                           *
#*********************************************************************
 F        = fixed_ren_scale  ! if .true. use fixed ren scale
 F        = fixed_fac_scale  ! if .true. use fixed fac scale
 91.1880  = scale            ! fixed ren scale
 91.1880  = dsqrt_q2fact1    ! fixed fact scale for pdf1
 91.1880  = dsqrt_q2fact2    ! fixed fact scale for pdf2
 1        = scalefact        ! scale factor for event-by-event scales
}}}


i.e., variable factorization and renormalization scales,set to the central mT^2 scale after kT-clustering of the event.
For a single heavy particle, this corresponds to the M^2+pT^2, 
for pair of heavy particles it is the geometric mean of M^2+pT^2 for each particle, 
for massless particles it is the pT^2 of the last pair after clustering. 
If the last clustering is a t-channel colorless exchange (as, e.g., in WBF),  the two fact. scales are set to the last mT^2 values on either side. 
These scales are overridden by scales defined in [http://cp3wks05.fynu.ucl.ac.be/cgi-bin/ViewVC/viewvc.cgi/MG_ME/Template/SubProcesses/setscales.f?view=markup setscales.f], if they are returned as non-0.

Fixed values for the scale (not event-by-event)  can be set in the same file, by setting the two flags {{{ fixed_ren_scale, fixed_fac_scale}}}  to True and choosing the desired value for them : {{{ scale, dsqrt_q2fact1, dsqrt_q2fact2 }}}


If the user wants to have a different choice for the dynamical scale, one needs

   1. to know a bit of fortran
   2. to download the code (either after process generation or from our Download page) and run on your local machine. 

The file to be edited is  [http://cp3wks05.fynu.ucl.ac.be/cgi-bin/ViewVC/viewvc.cgi/MG_ME/Template/SubProcesses/setscales.f?view=markup SubProcesses/setscales.f].



-- Main.FabioMaltoni - 02 Mar 2009