.. _user_interface:


User Interface 
=================

Users can log in to GRAVITON through the User Interface. To do this, simply execute via CLI:

.. raw:: html

    <pre style="border: 1px solid #ccc; padding: 10px; width: 100%; background-color: #fdf6e3"><code style="border: none"><strong><span >user@local:~</span></strong>$ ssh graviton_user@graviton.ific.uv.es</code></pre>

Automatically, we will enter the User Interface of GRAVITON.

.. code-block:: console
    
  ==========================================================
  Welcome to
   _____                     _  _    
  / ____|                   (_)| |
 | |  __  _ __  __ _ __   __ _ | |_  ___   _ __  
 | | |_ || '__|/ _  |\ \ / /| || __|/ _ \ | '_ \ 
 | |__| || |  | (_| | \ V / | || |_| (_) || | | |
  \_____||_|   \__,_|  \_/  |_| \__|\___/ |_| |_|

  The SOM's parallel computing infrastructure
  ==========================================================
  **Information**
  OS: AlmaLinux 9.2 (Turquoise Kodkod)
  MPI Version: mpirun (Open MPI) 4.1.5
  Job Scheduler: HTCondor V.23.1.0 
  Submision File Examples: /condor_submit_files_examples/ 
  Job Scheduler Manual: https://htcondor.readthedocs.io/ 
  ==========================================================
  **Useful Commands**
  CPUstatus: summary on CPU utilization
  ==========================================================

In this environment, we can develop code and perform tests directly via CLI, keeping in mind that only the 56 cores available in the User Interface will be used. If we want to utilize the power of the Worker Nodes, we must use the Job Scheduler of GRAVITON.


MPI Test example
----------------

Currently, version 4.1.5 of OpenMPI is installed on GRAVITON. Let's imagine we want to test the C++ code hello_world_mpi.cpp using the MPI library :code:`mpi.h`. The C++ script will have the following structure:

.. code-block:: C++

	#include <iostream>
	#include <mpi.h>

	int main(int argc, char** argv) {
    	MPI_Init(&argc, &argv);

    	int world_rank;
    	MPI_Comm_rank(MPI_COMM_WORLD, &world_rank);

    	int world_size;
    	MPI_Comm_size(MPI_COMM_WORLD, &world_size);

    	if (world_rank == 0) {
        	std::cout << "Hello World from the main process (rank 0) of " << world_size << " processes." << std::endl;
    	} else {
        	std::cout << "Hello World from process " << world_rank << " of " << world_size << "." << std::endl;
    	}

    	MPI_Finalize();

    	return 0;
	}

This is a simple code that launches the classic "hello world" across different cores. To work with it, we must use Open MPI. First, we compile the code using the Open MPI C++ compiler. The command used is :code:`mpicxx`. Here is an example:

.. raw:: html

    <pre style="border: 1px solid #ccc; padding: 10px; width: 100%; background-color: #fdf6e3"><code style="border: none"><strong><span style="color: green;">graviton_user@gr01:</span><span style="color: blue;">~</span></strong>$ mpicxx -o hello_world_mpi hello_world_mpi.cpp</code></pre>

Once compiled, we can now execute it and launch it across the number of cores we want. To execute this code directly in the CLI, we will use the command :code:`mpirun`:

.. raw:: html

    <pre style="border: 1px solid #ccc; padding: 10px; width: 100%; background-color: #fdf6e3"><code style="border: none"><strong><span style="color: green;">graviton_user@gr01:</span><span style="color: blue;">~</span></strong>$ mpirun -n 4 ./hello_world_mpi</code></pre>

In this example, we launch the code across 4 cores. The output we will obtain will be:

.. code-block:: bash

	Hello World from the main process (rank 0) of 4 processes.
	Hello World from the main process 2 de 4.
	Hello World from the main process 1 de 4.
	Hello World from the main process 3 de 4.


As already mentioned, GRAVITON allows for testing on the UI node, which has 56 cores. To utilize the Worker Nodes, it is necessary to use the queue manager HTCondor.