Neko  0.8.99
A portable framework for high-order spectral element flow simulations
Contributing to Neko

Please read the following guide before contributing new code or a bug fix to Neko.

All contributions to Neko must be made under the 3-Clause BSD license. Please refer to the COPYING file.

Git branches

Neko follows the Git branching model described in, where develop contains the latest contributions, and all pull requests should start from develop and be merged back into develop. New branches should be named feature/<description> for new features or fix/<description> for bug fixes.

When a pull request is submitted, a series of continuous integration tests will be run. A pull request will not be accepted nor merged into develop until it passes the test suite.

Code style

Fortran code should conform to the Fortran 2008 standard and should use an indentation level of 2, except for the extra indentation within do if, select or where statements and for each level inside a structure e.g. type, interface, where the indentation level is 3, and a 0 indentation is used for module or contains (except for contains inside a derived type, where a single indentation level is used). These are the default rules in Emacs' Fortran mode, an example is given below,

module example
use mod
implicit none
type :: derived_t
integer :: x
procedure, pass(this) :: bar
end type derived_t
subroutine foo(x, y)
integer, intent(in) :: x
integer, intent(inout) :: y
real(kind=rp) :: value
do i = 1, 10
end do
if (x .lt. y) then
end if
end subroutine foo
end module example

Please note that the maximum line length in Neko should not exceed 80 columns.

Data types

For portability reasons, it is essential to only use data type kinds defined in src/config/num_types.f90 and avoid legacy constructs like real*8 or integer(kind=8)

Floating-point numbers should be declared using real with the kind rp, which is the configured working precision for Neko (defaults to double). If single, double or quad precision is explicitly needed, use the kinds sp, dp or qp, respectively. For 16, 32, or 64-bit integers, Neko has defined the kinds i2, i4 or i8, respectively; however, for standard integers, it is perfectly fine to use a plain integer.

Build system

This section contains information on how to add new source files to the build system. Note that this section currently only covers Fortran code. It will be updated with information on how to add accelerator code and unit tests in a near future.

Neko uses Autotools for building all sources. You will need to have at least autoconf and automake installed for development work. It is also highly recommended to have makedepf90 installed to avoid error-prone manual dependency tracking.

The following steps describe how to add a new Fortran file to Neko's build system

  1. Place the file in an appropriate subdirectory under src/. Either create a new subdirectory or place the file in common if none of the existing directories is a good match. Avoid placing the file directly under src
  2. Add the file to the neko_fortran_SOURCES list in src/, following the pattern of <subdir under src>/newfile.f90.
  3. Ensure correct dependency tracking
    • Using makedepf90
      • Regenerate build system by running ./ at the top level, and reconfigure using configure
      • Regenerate dependency file (src/.depends) by issuing make depend under src
      • Do a final regeneration of the build system (./
    • Manually
      • Manually add the new file and all its dependencies to src/.depends, using the following pattern, ```Make directory/newfile.o : directory/newfile.f90 directory/dependency.o anotherdirectory/anotherdependency.o ``
      • Regenerate build system by running./regen.shat the top level.
  4. Finally reconfigure usingconfigure` and rebuild Neko with your new contribution!

For more information, please refer to the documentation

Happy hacking! 🍻