A minor issue with FCFAConvert

[DexKim]

• Your Mathematica version

  11.1.1 for Microsoft Windows (64-bit) (April 18, 2017)

• Your FeynCalc version

  9.2.0

• Did you try to reinstall FeynCalc (stable version) using the automatic installer to make sure that you have the latest bugfixes?

  Yes

• Please provide a minimal working example that illustrates the problem. Please explain the difference between the current behavior and the expected behavior.

The function FCFAConvert seems to have problems with substituting indices in FASUNF(a,b,c,d). For example, when the following code is evaluated

t4 = CreateTopologies[0, 4];
gggg = InsertFields[t4, {V[5], V[5], V[5], V[5]} -> {}, 
   InsertionLevel -> {Classes}, Model -> "SMQCD"];
ggggAmp = 
 FCFAConvert[CreateFeynAmp[gggg, PreFactor -> 1], 
  IncomingMomenta -> {p1, p2, p3, p4}, DropSumOver -> True, 
  SUNIndexNames -> {a, b, c, d, e}, 
  LorentzIndexNames -> {Subscript[\[Mu], 1], Subscript[\[Mu], 2], 
    Subscript[\[Mu], 3], Subscript[\[Mu], 4], Subscript[\[Mu], 5], 
    Subscript[\[Mu], 6]}]

the first amplitude comes up with a factor -f^($AL$14645cd) f^(ab$AL$14645)-f^($AL$14646bd) f^(ac$AL$14646) . Although the expression itself seems to be valid, the label $AL$(some number) is very odd.

[vsht]

Those are just dummy indices, so I don't really understand what is the problem here..

[DexKim]

I was wondering if those dummy indices could be given names that would be more familiar to the human eye. I thing I should just live with it...

[vsht]

Well, you sort of can do this like

ggggAmp[[1]] // FCCanonicalizeDummyIndices[#, Head -> {SUNIndex}] &

or

ggggAmp[[1]] // 
 FCCanonicalizeDummyIndices[#, SUNIndexNames -> {i1, i2}, 
   Head -> {SUNIndex}] &

but this is not a clever thing to do, unless it is meant for some teaching/demonstrating purposes, or you exactly know what you are doing. Canonicalization of dummy indices is a very expensive operation and should be usually avoided as much as possible. Moreover, it simply makes no sense to canonicalize indices that will be anyhow contracted in the step.