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pages/merlin7/05-Software-Support/cray-module.env.md

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+---
+title: Cray Programming Environment
+#tags:
+keywords: cray, module
+last_updated: 24 Mai 2023
+summary: "This document describes how to use the Cray Programming Environment on Merlin7."
+sidebar: merlin7_sidebar
+permalink: /merlin7/cray-module-env.html
+---
+
+## Loading the Cray module
+
+The Cray Programming Environment, with Cray's compilers and MPI, is not loaded by default.
+
+To load it, one has to run the following command:
+
+```bash
+module load cray
+```
+
+The Cray Programming Environment will load all the necessary dependencies. In example:
+
+```bash
+🔥 [caubet_m@login001:~]# module list
+Currently Loaded Modules:
+ 1) craype-x86-rome                                 2) libfabric/1.15.2.0
+ 3) craype-network-ofi                             
+ 4) xpmem/2.9.6-1.1_20240510205610__g087dc11fc19d   5) PrgEnv-cray/8.5.0
+ 6) cce/17.0.0                                      7) cray-libsci/23.12.5
+ 8) cray-mpich/8.1.28                               9) craype/2.7.30
+10) perftools-base/23.12.0                         11) cpe/23.12
+12) cray/23.12                                     
+```
+
+You will notice an unfamiliar `PrgEnv-cray/8.5.0` that was loaded. This is a meta-module that Cray provides to simplify the switch of compilers and their associated dependencies and libraries,
+as a whole called Programming Environment. In the Cray Programming Environment, there are 4 key modules.
+
+* `cray-libsci` is a collection of numerical routines tuned for performance on Cray systems.
+* `libfabric` is an important low-level library that allows you to take advantage of the high performance Slingshot network. 
+* `cray-mpich` is a CUDA-aware MPI implementation, optimized for Cray systems.
+* `cce` is the compiler from Cray. C/C++ compilers are based on Clang/LLVM while Fortran supports Fortran 2018 standard. More info: https://user.cscs.ch/computing/compilation/cray/
+
+You can switch between different programming environments. You can check the available module with the `module avail` command, as follows:
+
+```bash
+🔥 [caubet_m@login001:~]# module avail PrgEnv
+--------------------- /opt/cray/pe/lmod/modulefiles/core ---------------------
+
+PrgEnv-cray/8.5.0               PrgEnv-gnu/8.5.0                
+PrgEnv-nvhpc/8.5.0              PrgEnv-nvidia/8.5.0             
+```
+## Switching compiler suites
+
+Compiler suites can be exchanged with PrgEnv (Programming Environments) provided by HPE-Cray. The wrappers call the correct compiler with appropriate options to build 
+and link applications with relevant libraries, as required by the loaded modules (only dynamic linking is supported) and therefore should replace direct calls to compiler 
+drivers in Makefiles and build scripts.
+
+To swap the the compiler suite from the default Cray to GNU compiler, one can run the following.
+
+```bash
+🔥 [caubet_m@login001:~]# module swap PrgEnv-cray/8.5.0 PrgEnv-gnu/8.5.0
+
+Lmod is automatically replacing "cce/17.0.0" with "gcc-native/12.3".
+```