· FeynCalc

Name: Vladyslav Shtabovenko Date: 08/03/15-04:34:57 PM Z

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Hi Gang,

instead of

Coefficient[tmp, Pair[LorentzIndex[mu, D], LorentzIndex[nu, D]]]

you can use just

Coefficient[tmp, FCI[MTD[mu, nu]]]

As for your second question, have a look at

https://github.com/FeynCalc/feyncalc/wiki/FAQ#fci_fce

Cheers,
Vladyslav

Am 03.08.2015 um 16:26 schrieb Gang Li:
> Hello, Vladyslav,
>
> I’ve faced with a problem when I want to extract a particular term using the Mathematica function “Coefficeint”.
> Num = TR[(GSD[q] + m).(a + I*b*GA5).(GSD[q + pc] + m).(a +
*> I*b*GA5).(GSD[q + pa + pb] + m).GAD[mu].(GSD[q

pb] + m).GAD[*
> nu]] // Simplify
>
> tmp = Coefficient[Num, a*a] // Simplify
> ———————————————
> Coefficient[tmp, MTD[mu, nu]] = 0 (does not work!)
> _____________________________________________
>
> However,
> Coefficient[tmp, Pair[LorentzIndex[mu, D], LorentzIndex[nu, D]]]
> works well.
>
> Why does FeynCalc contain different input forms of the same expression?
>

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