home.md

@@ -282,6 +282,7 @@ module purge
 ```
 
 ## Compiling programs
+We are going to compile a very simple MPI (message passing interface) program, which is quite common on a cluster.
 - vi hello.c
 
 ```
@@ -308,8 +309,32 @@ int main (int argc, char *argv[])
 }
 ```
 
+If you are going to compile this program without the correct loaded module(s), you would see something like this:
+
+```
+$ module li
+No modules loaded
+$ gcc hello1.c -o hello1
+hello1.c:2:10: fatal error: mpi.h: No such file or directory
+ #include <mpi.h>
+          ^~~~~~~
+compilation terminated.
+```
+
+So we need to load the correct module:
+
+```
+$ module add pmi/openpmix/4.0.0/gcc-8.2.1
+```
+
 - mpicc hello.c -o hello
 
+Handy reference:
+
+| Language | C     | C++   | Fortran77 | Fortran90 | Fortran95 |
+| ---      | ---   | ---   | ---       | ---       | ---       |
+| Command  | mpicc | mpiCC | mpif77    | mpif90    | mpif95    |
+
 - ./hello
 
 ```