# Working with Fortran

The tutorial assumes you have already worked through the [Execute a Job Tutorial](/docs/using-the-hpc/execute-a-job.md). Therefore, the instructions here are abbreviated but will follow the same format so you may easily consult the extended tutorial.

**Table of Contents**

* [Step 1: Access the Onyx HPC](/docs/using-the-hpc/execute-a-job/fortran.md#step-1-access-the-onyx-hpc)
* [Step 2: Create an sbatch Script](/docs/using-the-hpc/execute-a-job/fortran.md#step-2-create-a-sbatch-script)
  * [Example sbatch Script](/docs/using-the-hpc/execute-a-job/fortran.md#example-sbatch-script)
  * [sbatch Procedure](/docs/using-the-hpc/execute-a-job/fortran.md#sbatch-procedure)
* [Step 3: Compile the Fortran Program from Source](/docs/using-the-hpc/execute-a-job/fortran.md#step-3-compile-the-fortran-program-from-source)
  * [MPI Hello World Source Code](/docs/using-the-hpc/execute-a-job/fortran.md#mpi-hello-world-source-code)
  * [Fortran Procedure](/docs/using-the-hpc/execute-a-job/fortran.md#fortran-procedure)
* [Step 4: Run the Job](/docs/using-the-hpc/execute-a-job/fortran.md#step-4-run-the-job)

📝 **Note:** Do not execute jobs on the login nodes; only use the login nodes to access your compute nodes. Processor-intensive, memory-intensive, or otherwise disruptive processes running on login nodes will be killed without warning.

## Step 1: Access the Onyx HPC

1. Open a Bash terminal (or MobaXterm for Windows users).
2. Execute `ssh doaneusername@onyx.doane.edu`.
3. When prompted, enter your password.

## Step 2: Create an sbatch Script

### Example sbatch Script

Here is an example sbatch script for running a batch job on an HPC like Onyx.

```bash
#!/bin/bash

#SBATCH -n 16
#SBATCH -o test_%A.out
#SBATCH --error test_%A.err
#SBATCH --mail-user $CHANGE_TO_YOUR_EMAIL
#SBATCH --mail-type ALL

module purge
module load gnu/5.4.0
module load openmpi
module list
mpirun hello_world_f
```

### sbatch Procedure

1. Use nano or Vim (we use Vim here) to create and edit your sbatch script.

   ```bash
   vim slurm_f90_example.job
   ```
2. Create your sbatch script within Vim by typing `i` for `insert` mode or paste the contents of your sbatch script into Vim.
3. Save your file by typing `:wq!` and return to the Bash shell.

## Step 3: Compile the Fortran Program from Source

### MPI Hello World Source Code

```
program helloworld
use mpi
integer ierr, numprocs, procid

call MPI_INIT(ierr)

call MPI_COMM_RANK(MPI_COMM_WORLD, procid, ierr)
call MPI_COMM_SIZE(MPI_COMM_WORLD, numprocs, ierr)

print *, "Hello world! I am process ", procid, "out of", numprocs, "!"

call MPI_FINALIZE(ierr)

stop
end
```

### Fortran Procedure

1. Use Vim (`vim`) to create your Fortran source file.

   ```bash
   vim hello_world.f90
   ```
2. Save your file and return to the Bash shell.
3. Load the MPI compiler using the openmpi module.

   ```bash
   module load openmpi
   ```
4. Compile the Fortran source into a binary executable file.

   ```bash
   mpifort -o hello_world_f hello_world.f90
   ```
5. Use `ls -al` to verify the presence of the `hello_world_f` binary in your working directory.

## Step 4: Run the Job

1. Before proceeding, ensure that you are still in your working directory (using `pwd`) and that you still have the PE-gnu module loaded (using `module list`).
   * We need to be in the same path/directory as our sbatch script and our Fortran binary. Use `ls -al` to confirm their presence.
2. Use `sbatch` to schedule your batch job in the queue.

   ```bash
   sbatch slurm_f90_example.job
   ```

   This command will automatically queue your job using slurm and produce a job number. You can check the status of your job at any time with the `squeue` command.

   ```bash
   squeue --job <jobnumber>
   ```

   You can also stop your job at any time with the `scancel` command.

   ```bash
   scancel --job <jobnumber>
   ```
3. View your results.\
   &#x20;You can view the contents of these files using the `less` command followed by the file name.<br>

   ```bash
   less test_<jobnumber>.out
   ```

   Your output should look something like this (*the output is truncated.*):

   ```bash
   Hello world! I am process            3 out of          20 !
   Hello world! I am process            0 out of          20 !
   Hello world! I am process            1 out of          20 !
   Hello world! I am process            7 out of          20 !
   Hello world! I am process            8 out of          20 !
   Hello world! I am process            2 out of          20 !
   Hello world! I am process            6 out of          20 !
   Hello world! I am process           11 out of          20 !
   .
   .
   .
   ```
4. Download your results (using the `scp` command or an SFTP client) or move them to persistent storage. See our [moving data](https://github.com/Doane-CCLA/docs/tree/47cc02e68a5d03cd2295c7babb1e9f0c7083e8d2/data-transfer-storage/moving-data.md) section for help.

#### Additional Examples

* [Working with C](/docs/using-the-hpc/execute-a-job.md)
* [Working with C++](/docs/using-the-hpc/execute-a-job/cpp.md)
* [Working with Python](/docs/using-the-hpc/execute-a-job/python.md)
* [Working with Makefiles](/docs/using-the-hpc/execute-a-job/makefile.md)


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