Software for calculating Feynman Diagrams Is there a software (open source preferred) where I would input something like "Ingoing: a fermion $(p1, s1)$ and a photon $(p2, s2)$. Output: A fermion $(k1, r1)$ and a photon $(k2, r2)$" and I would could then get each diagram (that is, each term in the Dyson series) up to whichever order I choose, also showing terms that evaluate to zero (just to see that they are there)?
I have tried to compute the above diagram to 2nd order and I'm just baffled with how many details there are to collect, this seems like the perfect job for a computer, but I can't find anything that would do such a symbolic calculation (hopefully showing the steps along the way) and not just the final result. 
 A: There are, of course, a lot of codes floating around. Which of them you should choose, depends on what you want to calculate exactly. Here I mention four possibilities:

*

*CALHEP - this package takes you from a given Lagrangian through its Feynmann rules to the calculation of cross sections.


*xloops - this package calculates the 1-PI Feynman diagrams with one and two closed loops for a given process in the Standard model and related theories.
Note added: as pointed out in the comments, the link does not work (as of July, 2021), will update this paragraph when a new link will be available.


*You should also take a look at MadGraph.


*And here is a nice paper that discusses how to generate and calculate one-loop Feynman diagrams with three software packages (each used at different steps). For example, it discusses the FormCalc package of FORM which was also mentioned by Hunter in his comment.
I hope some of these will help you with the particular calculation that you want to perform.
Edit. Let me add here also the comment of TomDickens, because this point should be stressed: Hopefully you know how to compute simple diagrams by hand already. These codes are not quite "black boxes".
