Using smatrix function in standalone mode ?

Asked by Tristan Beau


Is there a tutorial somewhere on how to use the
standalone version of MadGraph 4 or 5 because I didn't perfectly
understood the input of the smatrix function, of other function in C++
mode ?

 Thanks for your help,


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Olivier Mattelaer (olivier-mattelaer) said :

This output is mainly foreseen for theorist and for interface to external program.

In order to have an example of code.

You can do

cd SubProcesses/P0_XXXXXXXXXXXX

The program will return the square matrix element for a hard-coded phase-space point.
You can take a look at the file check_sa.f

This contains the driver and therefore the different step needed to configure the parameter,
the format for the 4 momentum, and how to call the square matrix element.

To be more precise, in fortran the Smatrix takes two argument:
1) P which are the momentum of the different particles
define as REAL*8 P(0:3,NEXTERNAL)
2) MATELEM which is in fact the output value (and therefore is a real*8)

Maybe if we knows what you plan to do, we can provide to you a bit more help.



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Tristan Beau (beau-3) said :

Ok, thanks. I didn't have a look to that check_sa source file. It's enough to understand how to call the matrix element function.

But one other related question. Is it possible to have a standalone version version including the management of pdf throw for example the lhapdf library, just like madevent can do ?

Thanks very much.



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Johan Alwall (johan-alwall) said :

Hello Tristan,

The Standalone package is meant as a minimal output, including only
what's necessary to calculate the matrix element. For ideas about how
to use PDFs with the matrix elements, I would recommend to look at the
MadEvent output code (in particular auto_dsigN.f+matrixN.f). You can
link this output to your private phase space integration code.

All the best,

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