Build Options¶
The shell script makenek is designed to assist the compilation process of Nek5000. The script will create a makefile based on the user settings section in makenek. The GNU gmake utility is used to build Nek5000.
Available configurations options:
| name | values | default | description |
|---|---|---|---|
| PPLIST | string | list of pre-processor symbols (CVODE, …) | |
| MPI | 1, 0 | 1 | use MPI (needed for a multiprocessor computation) |
| FC | string | optional | Fortran compiler (mpif77) |
| CC | string | optional | C compiler (mpicc) |
| FCLAGS | string | optional | optional Fortan compilation flags |
| CCLAGS | string | optional | optional C compilation flags |
| SOURCE_ROOT | string | optional | path of Nek5000 source |
| USR | string | optional | object list of additional files to compile make intructions (makefile_usr.inc required) |
| USR_LFLAGS | string | optional | optional linking flags |
| PROFILING | 1, 0 | 1 | enable internal timers for performance statistics |
| VISIT | 1, 0 | 0 | Toggles Visit in situ. See Visit_in_situ for details |
| VISIT_INSTALL | string | VISIT in situ | Path to VISIT install path. See Visit_in_situ for details. |
| VISIT_STOP | true, false | false | When running VISIT in situ, simulation stops after step 1 to connect VISIT. |
Preprocessor List¶
The PPLIST field can be used to activate several features at compilation time.
A list of possible options is shown in the table below.
For a comprehensive list of options available with your version of Nek5000, set PPLIST="?" and execute makenek.
| Symbol | Description |
|---|---|
| CVODE | compile with CVODE support for scalars |
| DPROCMAP | use distributed processor mapping |
| HYPRE | enable HYPRE support for AMG preconditioner (requires Cmake) |
| NOMPIIO | deactivate MPI-IO support |
| PARRSB | use online RSB partitioner |
| VENDOR_BLAS | use VENDOR BLAS/LAPACK |
| XSMM | use libxsmm for mxm |
The HYPRE symbol simplifies the use of the AMG preconditioner and is necessary to use any of the HYPRE pressure preconditioners as specified in the .par file.
This will download and install HYPRE V2.15.1.
An AMG preconditioner is necessary to run large (\(E>350,000\)) meshes.
The PARRSB symbol compiles Nek with the new online mesh partitioner.
This can be used along with the tool gencon as an alternative to genmap.
This is recommended for large (\(E>150,000\)) meshes.
The following options have been deprecated and are no longer available or necessary as of the latest version availble on github:
| Symbol | Description |
|---|---|
| BGQ | use Blue Gene Q optimized mxm (supported through V19) |
| EXTBAR | add underscore to exit call (supported through V17) |
| NEKNEK | activate overlapping mesh solver (supported through V17) |
| CMTNEK | activate discontinuous Galerkin (supported through V17) |
The NekNek capability has been fully integrated into Nek5000 and a preprocessor symbol is no longer necesary to use this feature.
Compiler Flags¶
In addition to these preprocessor items, the user can add compilation and linking flags.
FFLAGS allows the user to add Fortran compilation flags while CCFAGS allows the user to
add C compilation flags.
These will be compiler dependent and the user is encouraged to consult the manual of the compiler if specific options are needed/desired.
A commonly used flag is -mcmodel which allows for arrays of size larger than 2GB.
This option tells the compiler to use a specific memory model to generate code and store data.
It can affect code size and performance.
If your program has global and static data with a total size smaller than 2GB, -mcmodel=small is sufficient.
Global and static data larger than 2GB requires -mcmodel=medium or -mcmodel=large.