Originally posted by **armandlcz** December 12, 2022
Hello FeynCalc team and FeynCalc users!.
I'm trying to compute the following contraction:
Contract[ ( A[\[Mu],\[Nu],a,b,c,d] + B[\[Mu],\[Nu],a,b,c,d] ) * ( FVD[l,\[Rho]] FVD[l,\[Rho]] C[c,d,a,b] + B[\[Lambda],\[Delta],c,d,a,b] FVD[l,\[Lambda]] FVD[l,\[Delta]] ) ]
where the tensors A, B, C are made out of the metric tensor in D dimensions: MTD[ \[Mu] , \[Nu] ] and all their indices are Lorentz indices (even the a, b, c, d indices are Lorentz indices). When I compute it on my personal computer everything goes well, but when I try to compute it on another computer ( where I have just installed Mathematica 12.0 and FeynCalc 9.3.1) what I get is the next messagge:
'Contract: Error! Contract has encountered a fatal problem and must abort the computation. The problem reads: Something went wrong during prepareProductContractions.'
If I erase FVD[l,\[Rho]] FVD[l,\[Rho]] in the second factor then I don't get error anymore: I mean if I compute
Contract[ ( A[\[Mu],\[Nu],a,b,c,d] + B[\[Mu],\[Nu],a,b,c,d] ) * ( C[c,d,a,b] + B[\[Lambda],\[Delta],c,d,a,b] FVD[l,\[Lambda]] FVD[l,\[Delta]] ) ]
don't get error. I have the same error when I try to compute other similar contractions. The same error appears when trying to contract many indices and only in the computer where I have just installed Mathematica (in my personal computer I don't get this error. I have to use the first computer because it's a too heavy calculation for my personal computer). I looked for a solution on the forum but I didn't find any topic about this.
I hope you can help me. Thanks a lot.
Both computers have Mathematica 12.0 and FeynCalc 9.3.1 (stable version).
Discussed in https://github.com/orgs/FeynCalc/discussions/204