**Note: on systems with no `sudo` access, one can replace `./configure` with `./configure prefix=${PWD}/_install` in order to execute `make install/uninstall` commands without `sudo` privileges.**
The `make install` command takes care of installing the TREXIO shared library on the user machine.
Once installed, add `-ltrexio` to the list of compiler options.
In some cases (e.g. when using custom `prefix` during configuration), the TREXIO library might end up installed in a directory, which is absent in the default `$LIBRARY_PATH`.
In order to link the program against TREXIO, the search paths in the current shell can be modified as follows: `export LIBRARY_PATH=$LIBRARY_PATH:<path_to_trexio>/lib` (same holds for `$LD_LIBRARY_PATH`). Do not forget to change `<path_to_trexio>`.
If your compilation relies on some build tools (like Autotools or CMake), feel free to use the built-in functions to locate and link external dependencies automatically.
In Fortran applications, make sure that the `trexio_f.f90` module file is included in the source tree.
You might have to manually copy it into your program source directory.
The `trexio_f.f90` module file can be found in the `include/` directory of the TREXIO source code distribution.
**Note:** there is no need to include `trexio.h` header file during compilation of Fortran programs.
Only the installed library and the Fortran module file are required.
For example, consider the `coord` variable (array), which belongs to the `nucleus` group. The TREXIO user can write or read it using `trexio_write_nucleus_coord` or `trexio_read_nucleus_coord` functions, respectively.
Note: the `[variable]` names have to be unique only within the corresponding parent `[group]`.
There is no naming conflict when, for example, `num` variable exists both in the `nucleus` group (i.e. the number of nuclei) and in the `mo` group (i.e. the number of molecular orbitals).
These quantities can be accessed using the corresponding `trexio_[has|read|write]_nucleus_num` and `trexio_[has|read|write]_mo_num`, respectively.
[TREX: Targeting Real Chemical Accuracy at the Exascale](https://trex-coe.eu) project has received funding from the European Union’s Horizon 2020 - Research and Innovation program - under grant agreement no. 952165. The content of this document does not represent the opinion of the European Union, and the European Union is not responsible for any use that might be made of such content.
