change matrix.f to include the choice of helicity/color within that file.

[oliviermattelaer]

Idea

update the fortran code to have the same interface as for GPU and therefore avoid to put the JAMP2 in a common block

• avoid to have to transfer it from GPU to CPU
• good time to test the low memory selection of color to avoid to have all jamp2 in memory at the same time (see #17)

Todo:

• [x] change signature of smatrix
  • [x] without helicity recycling
    • [ ] pass to the low memory mode (see #17)
  • [x] wih helicity recycling
    • [ ] check if relevant to use the low memory mode (see #17)
• [ ] change the signature of matrix
  • [ ] without helicity recycling
• [x] change addmothers.f
• [x] change the events writing
  • [x] temporary format (avoid the use of buffer)
  • [x] final format

[oliviermattelaer]

note

    CHARACTER*101         HEL_BUFF
    COMMON/TO_HELICITY/  HEL_BUFF
 WRITE(HEL_BUFF,'(20i5)')(NHEL(II,I),II=1,NEXTERNAL)

(need to be replaced via the call to ihel) -> need to have a function get_helicity(iproc, ihel) call get_helicity(iproc, ihel, nhel) that calls get_nhelX(...)

[oliviermattelaer]

case without plugin/helicity recycling/mlm implemented here:

https://github.com/mg5amcnlo/mg5amcnlo/commit/0587cbbd549c053414beb4ecf0b5883047a1a9a4 following commit is make the change consistent with helicity recycling https://github.com/mg5amcnlo/mg5amcnlo/commit/18a90f58587e3a7b07610b9ed5780695d094a76c

[oliviermattelaer]

Validation:

• [x] check that the code compile
• [x] check that the cross-section is correct
• [x] Helicity
  • [x] are filled
    • [x] returned non zero from smatrix
    • [x] are passed non zero (and same as smatrix) to write_leshouches
    • [x] are returning non zero from the new function for getting the helicity
      • function return 0 0 0 0 in last commit
  • [x] have correct rate
    • wrong with helicity recycling since the index is remapped to not have "hole" (fixed in https://github.com/mg5amcnlo/mg5amcnlo/commit/3622a74e42e00d97d4877f1b5985754e40baf2d1)
• [x] Color
  • [x] are filled
  • [x] have correct rate
• [x] JAMP2
  • [x] check that all jamp2 have been removed from memory (especially the vectorised version)