Name: Peter Blunden (email_not_shown)
Date: 03/20/03-10:56:18 PM Z


There have been previous messages about a bug in the evaluation of
Tr[DiracSlash[p,p]] giving p^2 instead of 4p^2. Rolf posted a fix, which
is incorporated into the new version. I have the new version, but still
get p^2 as the answer. However, Purnendu Chakraborty, responding to a
query by Roberto Sghedoni, claimed to get 4p^2.

So what is going on? How can 2 people running the same version get
different answers? In exploring this, I stumbled across a bizarre bug. The
answer is that it depends on how FeynCalc is loaded!

For example, loading FeynCalc.m directly, one gets the right answer:

In[1]:= <<FeynCalc.m

FeynCalc4.1.1 Type ?FeynCalc for help or visit http://www.feyncalc.org
$PrePrint is set to FeynCalcForm. Use FI and FC to change the display
format.

In[2]:= Tr[DiracSlash[p,p]]

           2
Out[2]= 4 p

However, loading FeynCalc in the recommended way gives the wrong answer:

In[1]:= <<HighEnergyPhysics`FeynCalc`

FeynCalc4.1.0.3b Type ?FeynCalc for help or visit http://www.feyncalc.org
$PrePrint is set to FeynCalcForm. Use FI and FC to change the display
format.

In[2]:= Tr[DiracSlash[p,p]]

         2
Out[2]= p

What gives? Peter



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