I want to simplify some expressions like a[i]*b[i]*KD[i,j]. After contraction, it should be a[j]*b[j], but it seems that FeynCalc cannot handle more than 3 of the same CartesianIndices.
I know for contraction it is not well defined. But what I just want to do is symbolically change a[i]*b[i] to a[j]*b[j]
Sorry, but this is not going to work. FeynCalc inherently relies on Einstein's summation convention, so every attempt to use the program on expressions violating it will generate inconsistent or simply wrong output.
What you will get for your input is, in fact, a[j] b[i] and not a[j] b[j]
DataType[a, FCTensor] = True;
DataType[b, FCTensor] = True;
a[CartesianIndex[i]]*b[CartesianIndex[i]]*KD[i, j]
% // Contract
