Fortran Style Guide

Naming Convention

Ultimately this is a matter of preference. Here is a style guide that we like and that seems to be prevalent in most scientific codes (as well as the Fortran standard library), and you are welcome to follow it.

  1. Use lowercase for all Fortran constructs (do, subroutine, module, …).

  2. Follow short mathematical notation for mathematical variables/functions (Ylm, Gamma, gamma, Enl, Rnl, …).

  3. For other names use all lowercase: try to keep names to one or two syllables; if more are required, use underscores to clarify (sortpair, whitechar, meshexp, numstrings, linspace, meshgrid, argsort, spline, spline_interp, spline_interpolate, stoperr, stop_error, meshexp_der).

For example “spline interpolation” can be shortened to spline_interpolation, spline_interpolate, spline_interp, spline, but not to splineint (“int” could mean integration, integer, etc. — too much ambiguity, even in the clear context of a computational code). This is in contrast to get_argument() where getarg() is perfectly clean and clear.

The above are general guidelines. In general, choosing the right name certainly depends on the word being truncated as to whether the first syllable is sufficient. Usually it is but clearly not always. Thus some thought should go into step “try to keep names to 2 syllables or less” since it can really affect the indicativeness and simplicity. Simple consistent naming rules are a real help in this regard – for both collaboration and for one’s own sanity when going back to some old code you haven’t seen in while.


Use a consistent indentation to make your code readable. The amount of indentation is a matter of preference, the most common choices are two, three or four spaces.

Comparison to Other Languages

On the other hand, in most of the rest of the programming world, where the main focus is, in one form or another, on defining and using large sets of complex objects, with tons of properties and behaviors, known only in the code in which they are defined (as opposed to defined by the same notation throughout the literature), it makes more sense to use longer, more descriptive names. The naming conventions one sees used in more general-purpose languages such as C++ and Python, therefore, are perfectly consistent with their more general-purpose missions. But Fortran has a different mission (numerical scientific computing).