Name: Vladyslav Shtabovenko Date: 04/08/15-03:03:24 PM Z

Dear FeynCalc users,

the new commit

<https://github.com/FeynCalc/feyncalc/commit/9365d4937c208d53d843568bb059f48e83cd3c26>

to the git repository of FeynCalc introduces a lot of changes to the
structure of FeynCalc that we would like to introduce in details here:

1) You might have been wondering, why FeynCalc must be installed to the
directory “HighEnergyPhysics” and not just “FeynCalc”. Well, this used
to be liked that for some legacy reasons but is actually not necessary
nowadays. From now on FeynCalc lives in “FeynCalc” and
it is started simply via “<<FeynCalc`”

2) The internal structure of FeynCalc got completely refactored to
simplify the maintenance and avoid problems with Mathematica’s
autocompletion. Before that FeynCalc actually consisted of hundreds of
separate packages (each .m file was a package). Loading that number of
packages in one session was freezing Mathematica’s auto-complete. This
should not occur anymore. Now FeynCalc is just one package and all its
objects live in the context HighEnergyPhysics`FeynCalc`. This allows us
to get rid of the (error-prone) tricks with MakeContext and CheckContext
that we had in the source code before. Furthermoe, the directory
structure was adjusted to be compatible with the standard layout in
Wolfram Workbench, which is the state of the art tool to develop large
Mathematica packages.

3) Much of the source code (although not everything yet) is now nicely
formatted.

4) The directory structure inside HighEnergyPhysics is now organized in
the following way
* “AddOns”: small user addons for FeynCalc
* “Database” : contains cached results for user’s computations
* “Dirac”: tools for Dirac algebra
* “Documentation”: contains package documentation
* “Examples”: sample computations with FeynCalc that reproduce known
results from the literature
* “ExportImport”: tools for exchanging results between FeynCalc and
other tools
* “FeynArts”: contains patched FeynArts
* “Feynman” : tools for dealing with S-matrix elements, including
derivation of Feynman rules and computation of the matrix element squared
* “Kernel”: related to the way Mathematica loads packages
* “LoopIntegral”: tools for loop integrals
* “Lorentz”: tools for working with quantities that carry Lorentz
indices and for dealing with the kinematics
* “Misc” : for routines that don’t fall into any other category.
* “NonComAlgebra”: general functions for non-commutative objects
* “Phi”: contains Frederik Orellana’s PHI
* “QCD” : tools for QCD OPE calculations (still poorly tested and
documented)
* “Shared”: general objects (e.g. Pair, DiracGamma, SUNF) and functions
(e.g. FreeQ2, SelectFree, Factor2) that are widely used by other parts
of the FeynCalc code.
* “SUN”: tools for SU(N) algebra
* “Tables”: database with various analytic expressions
* “Phi”: contains TARCER by Rolf Mertig and Rainer Scharf

5) Since FeynCalc now always loads all its .m files, we squashed some
(short) functions into common files. For example, Apart1, Apart2 and
Apart3 now live in Apart.m. This is done to keep the time FeynCalc needs
to load reasonably small.

6) Options parsing in many functions have been improved to use the
modern MMA’s OptionsPattern - OptionValue paradigm.

7) The number of unit tests have been increased. Although we are still
far away from the full code coverage, with more than 2700 unit test we
are doing quite good.

8) FeynCalc tabulates many expressions that can be requested by the
user, e.g. Lagrangians. To make it easy for the user to work with these
expressions, FeynCalc returned them with indices and variables in the
Global` context. However this also means that when FeynCalc is loaded,
it puts a lot of objects into the Global` context where they may clash
with user-defined functions. To solve this problem we introduced a new
object: FCGV which is acronym for FeynCalc Global Variable. The syntax
is FCGV[x_String]. From now on, variables that used to be returned as
Global`VariableName will be outputted as FCGV[“VariableName”]. You will
nottice them in your expressions as having FCGV around them, i.e.
FCGV[“p”] will be displayed as FCGV(p). You can always convert such
objects to “normal” variables via the replacement rule {FCGV[x_String]
:>ToExpression[x]} We understand that this additional step may pose some
inconveniences to you, but from the point of view of Mathematica
programming and interoperability between different packages, this
solution seems to be the cleanest way to avoid troubles in future.

For example, Lagrangian[“QCD”] now returns

-(1/4) FieldStrength[FCGV[”\[Alpha]”], FCGV[”\[Beta]”],
   FCGV[“a”]].FieldStrength[FCGV[”\[Alpha]”], FCGV[”\[Beta]”],
   FCGV[“a”]]

instead of

-(1/4) FieldStrength[\[Alpha], \[Beta],
   a].FieldStrength[\[Alpha], \[Beta], a]

as it used to be. Now suppose that before invoking Lagrangian[“QCD”] you
defined \[Alpha] = 1/137. With the new output using FCGV nothing
changes. With the old output
you would have got

-(1/4) FieldStrength[1/137, \[Beta], a].FieldStrength[1/137, \[Beta], a]

which is clearly not what you want.

9) To circumvent problems related to the patching of FeynArts, from now
on FeynCalc will look for FeynArts only in the directory “FeynArts”
inside “HighEnergyPhysics”. Nevertheless, it is still possible to
specify an alternative directory by setting
FeynCalc`$FeynArtsDirectory=”path” before loading FeynCalc. The patching
code was moved to FeynCalc, i.e. now it will run even when Phi is not
loaded.

10) The TARCER notebook have been converted into a source file
(“TARCER.m”). Furthermore, generated TARCER*.mx files are not
distributed anymore with the source code. When you first try to load
TARCER, a dialog will appear with the suggestion to generate the .mx
file now. This process has to be done only once and takes only a couple
of minutes. After that, the generated .mx will be automatically loaded
whenever you want to use TARCER.

11) Prior to this commit FeynCalc used to switch the format of output
cells to TraditionalForm. Now it will only issue a
warning message suggesting the user to do this by himself or herself.
Such messages can be disabled by setting $FCAdvice to False.
So if you despise all the fancy typesetting and prefer to work with
StandardForm, FeynCalc will respect your decision.

12) To avoid clashes with built-in functions of recent Mathematica
versions, we had to rename
some FeynCalc functions:

PartialD -> FCPartialD
Symmetrize -> FCSymmetrize
AntiSymmetrize -> FCAntiSymmetrize

Cheers,
Vladyslav