Name: Vladyslav Shtabovenko (email_not_shown)
Date: 04/15/15-05:08:53 PM Z


Dear Samuel,

> 1) it exist, but it does not appear in the online manual
> http://feyncalc.org/FeynCalcBook/

The online manual is unfortunately somewhat outdated. If you click on
"help browser" in the message that appears when FeynCalc loads, you can
use the integrated documentation, which also contains Schouten.

> 2) acting on a given expression A with Schouten[Calc[A]] is fine
> (my expression is 0 after using Schouten, as it should),
> but if I do SetOptions[Contract, Schouten -> True]
> or SetOptions[Calc, Schouten -> True] (in practice Calc,
> so SetOptions[Contract, Schouten -> True] should be enough),
> my expression does not vanish without using Calc.
> Why?

In this case the option Schouten specifies the maximal number of terms
in the expression to apply the Schouten identity (evaluate ?Schouten).
By default it is 0, i.e. the identity is not applied. You can set it to
say 100 or 1000 to be sure that it will be always applied. Here is an
example from the manual:

t = Sum[Sum[(SP[k,
       q[a]] (1/
        6 Eps[LorentzIndex[a], LorentzIndex[b], LorentzIndex[c],
         LorentzIndex[d]] Eps[LorentzIndex[mu], Momentum[q[b]],
         Momentum[q[c]], Momentum[q[d]]])), {a, 1, 4}], {b, 1, 4}, {c,
     1, 4}, {d, 1, 4}] -
  Eps[Momentum[q[1]], Momentum[q[2]], Momentum[q[3]], Momentum[q[4]]]*
   Pair[LorentzIndex[mu], Momentum[k]]

Contract[t] is not zero, but Contract[t, Schouten -> 100] indeed vanishes.

Bien cordialement,
Vladyslav

Am 15.04.2015 um 16:50 schrieb Samuel Wallon:
> Dear Vladyslav,
> I have a problem with the use of the Schouten identity:
>
> 1) it exist, but it does not appear in the online manual
> http://feyncalc.org/FeynCalcBook/
>
> 2) acting on a given expression A with Schouten[Calc[A]] is fine
> (my expression is 0 after using Schouten, as it should),
> but if I do SetOptions[Contract, Schouten -> True]
> or SetOptions[Calc, Schouten -> True] (in practice Calc,
> so SetOptions[Contract, Schouten -> True] should be enough),
> my expression does not vanish without using Calc.
> Why?
>
> Thanks in advance for your help.
>
> Best
>
> Samuel Wallon
>
> =============================================================
> Samuel.Wallon@th.u-psud.fr
>
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>
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