Changes between Version 5 and Version 6 of FAQ-General-4

Timestamp:

Oct 6, 2017, 9:01:05 PM (8 years ago)

Author:

Olivier Mattelaer

Comment:

--

FAQ-General-4

@@ -14 +14 @@
 }}}
 
+=== Pythton
+
 If you want to have acces to the matrix-element via python. The easiest is to have the fortran code wrapped into python (evaluating a matrix element in python is just too slow to be usable). Each of the SubProcesses/P_xx_xxxx of the standalone directory can be compiled to be python linkable (note this require f2py part of numpy and to have python-devel package installed):
 {{{
@@ -20 +22 @@
 
 Then you can link this from your python code. Here is an example:
+{{{
+import matrix2py
+
+def invert_momenta(p):
+        """ fortran/C-python do not order table in the same order"""
+        new_p = []
+        for i in range(len(p[0])):  new_p.append([0]*len(p))
+        for i, onep in enumerate(p):
+            for j, x in enumerate(onep):
+                new_p[j][i] = x
+        return new_p
+
+matrix2py.initialisemodel('../../Cards/param_card.dat')
+p = [[   0.5000000E+03,  0.0000000E+00,  0.0000000E+00,  0.5000000E+03],
+     [   0.5000000E+03,  0.0000000E+00,  0.0000000E+00, -0.5000000E+03],
+     [   0.5000000E+03,  0.1109243E+03,  0.4448308E+03, -0.1995529E+03],
+     [   0.5000000E+03, -0.1109243E+03, -0.4448308E+03,  0.1995529E+03]]
+
+P =invert_momenta(p)
+alphas = 0.13
+nhel = -1 # means sum over all helicity                                                                                                                                                                   
+me2 = matrix2py.get_value(P, alphas, nhel)
+print me2
+}}}
+
+=== Full library of process in python
+
+If you are interested to have a single python library for a set of matrix-element.
+This is also possible in fortran/python.
+This is possible both for loop output ([sqr=virt]) and for tree level.
+{{{
+   generate p p > t t~
+   output standalone PATH --prefix=int
+}}}
+
+then you can compile the library by going to the SubProcesses  directory and 
+{{{
+make allmatrix2py.so
+}}}
+
+Here is one example in that case
+{{{
+import allmatrix2py
+allmatrix2py.initialise('../Cards/param_card.dat')
+
+def invert_momenta(p):
+        """ fortran/C-python do not order table in the same order"""
+        new_p = []
+        for i in range(len(p[0])):  new_p.append([0]*len(p))
+        for i, onep in enumerate(p):
+            for j, x in enumerate(onep):
+                new_p[j][i] = x
+        return new_p
+p =[[  0.5000000E+03,  0.0000000E+00,  0.0000000E+00,  0.5000000E+03],
+    [0.5000000E+03,  0.0000000E+00,  0.0000000E+00, -0.5000000E+03],
+    [ 0.5000000E+03,  0.1040730E+03,  0.4173556E+03, -0.1872274E+03],
+    [ 0.5000000E+03, -0.1040730E+03, -0.4173556E+03,  0.1872274E+03]
+    ]
+
+p =invert_momenta(p)
+nhel = -1 # means sum over all helicity
+pdgs = [21,21,6,-6] #which pdg is requested
+scale2 = 0.  #only used for loop matrix element. should be set to 0 for tree-level
+alphas=0.13
+
+ans = allmatrix2py.smatrixhel(pdgs,p,alphas,scale2,nhel)
+print ans
+}}}
+
+=== Python for version MG5_aMC version 2.5.x
+
+For version of the code older than 2.6.0, the syntax was:
+
 {{{
 import matrix2py