The following are coding conventions employed in Galacticus' source code.

Variable names

• Variable names use camelCase form;
• Variable names should be descriptive, massStellarDisk is preferred over m, or mass for example;

Matching parameter names

• For variables which are set via a parameter, the internal variable name should match the parameter name. (This allows automatic handling of the creation of descriptor functions). In some cases this is not possible if the parameter name matches the name of a method of the class. For example, the stellarFeedbackOutflowsPowerLaw class has a method velocityCharacteristic, and also reads a parameter of this name. In such cases the internal variable name should match the parameter name with a _ suffix. This convention allows such variables to be correctly included in the creation of descriptor functions.

Function classes

functionClass objects are the primary object class used within Galacticus to represent physical processes and other actors.

Formatting

Variable declarations

• Only two variables per line, use continuation lines for more than two variables, i.e. instead of:

    logical                   , intent(  out)                            :: diskRequired, spheroidRequired, radiusVirialRequired, radiusScaleRequired

write

    logical                   , intent(  out)                            :: diskRequired        , spheroidRequired   , &
         &                                                                  radiusVirialRequired, radiusScaleRequired

Comments

LaTeX vs. Unicode

Comments inside !!{ !!} sections should use LaTeX syntax (as they are directly rendered into the documentation which is built using LaTeX. Comments outside of these sections should avoid LaTeX syntax where possible, and instead use unicode symbols. For example, use ! km s¯¹ instead of ! km s^{-1}.

Citations

Where relevant, include citations to papers in comments. For example, before a line implementing an equation from a paper, include a comment line:

! Critical mass model from Author1 & Author2 (2015; http://.......).

It is preferred that the URL be to the NASA ADS entry for the paper if possible.

Citations should also be given in class description elements also - for example if a class implements a model from a specific paper cite that paper in the description, e.g.:

  <nodeOperator name="nodeOperatorFunPhysics">
   <description>A node operator that implements some fun physics. Based on the model of \cite{funPhysicsPaper}.</description>
  </nodeOperator>

and include a bibliography entry in docs/Galacticus.bib for this paper (this will then be automatically included into the documentation). Note that the preferred way to add entries to the bibliography is to first add the relevant NASA ADS record to the Galacticus Zotero library, and then export from there into docs/Galacticus.bib.

Constants

• Floating point constants should be written as explicitly double precision, so 7.0 should be 7.0d0 for example.
• Avoid arbitrary numbers appearing in the code, e.g. instead of 3.2408d-14, define a variable that has a descriptive name, e.g.:

double precision, parameter :: importantPhysicalConstant=3.2408d-14

so that it is obvious to what this number refers.

Unit Conversion Constants

Defined constants that convert between units should follow the naming convention: unitAToUnitB which implies that multiplying a quantity in units of unitA by unitAToUnitB will give that same quantity in units of unitB. For example, the constant metersToAngstroms$=10^{10}$ when multiplying a length in meters will give the corresponding length in Angstroms.

Indicating Units of Defined Constants

The unit system in which a constant is defined should be indicated by a suffix starting with an underscore. The default, which requires no suffix, is the SI system. So, for example, the defined constant massSolar (which has no suffix) will be in SI units of kilograms. The defined constant lymanSeriesLimitWavelengthHydrogen_atomic is in the "atomic" unit system, so will be in units of Angstroms.

Currently, defined unit systems are:

• no suffix: With no suffix, the defined constant is in the [SI[(https://en.wikipedia.org/wiki/International_System_of_Units) unit system.
• _internal: The "internal" suffix indicates a defined constant is in Galacticus's internal unit system of $\mathrm{M}_\odot$, Mpc, Gyr, and km/s.
• _atomic: The "atomic" suffix indicates atomic units (Å).
• _cgs: The "cgs" suffix indicates a defined constant is in the CGS unit system.