Building Nyx with GNU Make¶

Nyx is built on top of the AMReX framework so you must download AMReX in order to build Nyx with GNU Make.

Clone/fork the AMReX repository:
```
git clone https://github.com/AMReX-Codes/amrex
```
You will want to periodically update AMReX by typing
```
git pull
```
in the amrex/ directory.

Note

When you check out AMReX (and Nyx), you will get the development branch. Active development is done on this branch; monthly tags are made of this version that are compatible with the same monthly tag of AMReX itself.

Set the environment variable AMREX_HOME to point to your local copy of the AMReX repository. You can add this to your .bashrc as:
```
export AMREX_HOME=/path/to/amrex/
```
or to your .cshrc as:
```
setenv AMREX_HOME /path/to/amrex/
```
where /path/to/amrex/ is the full path to the amrex directory.
Clone/fork the Nyx repository:
```
git clone https://github.com/AMReX-Astro/Nyx
```
As with AMReX development on Nyx is done in the development branch, so you should work there if you want the latest source.
Choose which executable to compile, for example MiniSB or LyA.

MiniSB is a small version of the Santa Barbara problem, and LyA is a Lyman-\(\alpha\) forest simulation for investigating the large-scale structure formation of the universe.

For some executables, namely LyA, AMR-density, AMR-zoom, and LyA_Neutrinos, Nyx uses a more complicated model for the heating-cooling. This requires you to also install a matching sundials installation to support the ODE solve. To install a stand-alone copy of Sundials, see Compiling Nyx with SUNDIALS 5
From the directory in which you checked out Nyx, change directory to your build directory by typing for the small Santa-Barbara problem:
```
cd Nyx/Exec/MiniSB
```
or for the Lyman-\(\alpha\) problem:
```
cd Nyx/Exec/LyA
```
In your build directory, edit the GNUmakefile, and set

COMP = your favorite compiler (e.g, gnu, Intel)

DEBUG = FALSE

We like COMP = gnu.

More information on the AMReX GNU Make setup can be found here.

All executables should work with MPI+CUDA by setting USE_MPI=TRUE USE_OMP=FALSE USE_CUDA=TRUE.

HIP and DPC++ builds are under development and can be tested by compiling with USE_HIP=TRUE and USE_DPCPP=TRUE respectively.

Note

For executables with USE_HEATCOOL=TRUE in their GNUmakefile, a matching Sundials implementation is required. If Sundials is built with -DSUNDIALS_BUILD_PACKAGE_FUSED_KERNELS=ON, Nyx should be built with USE_FUSED=TRUE. The flag USE_FUSED tells the Nyx compile whether you compiled Sundials with fused cuda kernels. The default assumption is that non-cuda Nyx compiles set USE_FUSED=FALSE to match Sundials being built without fused cuda kernels. Starting with Sundials version 5.7.0, set USE_SUNDIALS_SUNMEMORY=TRUE to compile the optional Sundials SunMemory to AMReX Arena interface for GPU memory reuse.
Now type “make”. The resulting executable will look something like “Nyx3d.Linux.gnu.ex”, which means this is a 3-d version of the code, made on a Linux machine, with COMP = gnu.

Note that if you build with USE_MPI = TRUE in the GNUMakefile, then the name of the code will be something like “Nyx3d.Linux.gnu.MPI.ex”