Name: Peter Blunden 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