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# SCCS Colloquium

The SCCS Colloquium is a forum giving students, guests, and members of the chair the opportunity to present their research insights, results, and challenges. Do you need ideas for your thesis topic? Do you want to meet your potential supervisor? Do you want to discuss your research with a diverse group of researchers, rehearse your conference talk, or simply cheer for your colleagues? Then this is the right place for you (and you are also welcome to bring your friends along).

# Rihab Torjmen: Implementation of Sparse-GEMM-Kernel for ADER-DG in SeisSol on GPUs

SCCS Colloquium |

Despite the fact that many researches have been done on the subject of how important is the
multiplication of a sparse matrix with a dense matrix, which is an paramount tool in the area
of computing and machine learning, the most efficient way to do it is still needed to be defined
since the process is full of challenges. The major goal of this research is to multiply dense x
sparse matrices using the GPU advantage of being able to compute it in more practical and
faster way. SeisSol, an application for earthquakes simulations and a scientific software for
the numerical simulation of seismic wave phenomena and earthquake dynamics, is the project
for which we are developing solutions. It is based on the the Arbitrary high-order DERivatives
Discontinuous Galerkin (ADER-DG), which is used to solve the issue of combined
elastodynamic wave propagation and dynamic rupture methods.[2] Seissol essentially helps
us predict earthquakes, which is a really innovative study field because it is already so difficult
to predict earthquakes, and it will actually help save people’s lives and issue warnings of
potential harmful earthquakes ahead of schedule enough to allow right approach to the
disaster, allowing people to minimize loss of life and destruction.[3]
ADER-DG methods are based on elements and expressions which are built on small matrices
that could be divided in two types: dense and sparse. If done correctly, using a sparse matrix
to accomplish the multiplication is much faster compared to the normal way, especially in our
project, since the sparsity pattern is giving in advance and for most cases, even the values are
provided to the user (It is actually delivered either during runtime or during compilation).
The issue with this multiplying procedure is that using the CPU or executing conventional
straight multiplication between the matrices is inefficient and wastes a lot of memory. As a
result, in our scenario, we'll use the GPU and do a different type of multiplication to have a
better performance. During previous projects, the multiplication of two dense matrices has
been done and it has been proven how less time consuming and more efficient it is, to use the
GPU instead of the CPU to get the job done.
The SeisSol numerical scheme essentially consists of sparse and dense small matrix
multiplications, where small is defined as the number of entries per dimension in the matrices
being less than 100. [19] Additionally, a priori knowledge of all sparsity patterns exists. We
define the architecture we want to optimize for and the convergence order, which results in
various matrix sizes, prior to executing SeisSol. Then, for each matrix multiplication, we obtain
specific matrix multiplication routines via our code generator.
A dense x dense, dense x dense, or sparse x sparse multiplication might apply to each of them.
We hardcode the sparsity pattern into the resulting code and arrange the operations in such
a way that the compiler automatically vectorises them when the matrix multiplication is
sparse. The dense x sparse multiplication will be included during this research study to extend
the concept and come closer to the eventual aim of being able to anticipate any sort of
earthquake.

Bachelor's thesis presentation. Rihab is advised by Ravil Dorozhinskii.

You don't want to miss a talk? Subscribe to our mailing list and our Colloquium calendar .

## Contribute a talk

To register and schedule a talk, you should fill the form Colloquium Registration at least two weeks before the earliest preferred date. Keep in mind that we only have limited slots, so please plan your presentation early. In special cases, contact colloquium@mailsccs.in.tum.de.

Colloquium sessions are now on-campus. We have booked room MI 00.13.054 for WS22/23. You can either bring your own laptop or send us the slides as a PDF ahead of time. The projector only has an HDMI connection, so please bring your own adapters if necessary.

Do you want to attend but cannot make it in person? We now have a hybrid option. Simply join us through this BBB room: https://bbb.in.tum.de/ger-wtc-qmp

We invite students doing their Bachelor's or Master's thesis, as well as IDP, Guided Research, or similar projects at SCCS to give one 20min presentation to discuss their results and potential future work. The time for this is typically after submitting your final text. Check also with your study program regarding any requirements for a final presentation of your project work.

New: In regular times, we will now have slots for presenting early stage projects (talk time 2-10min). This is an optional opportunity for getting additional feedback early and there is no strict timeline.

Apart from students, we also welcome doctoral candidates and guests to present their projects.

During the colloquium, things usually go as follows:

• 10min before the colloquium starts, the speakers setup their equipment with the help of the moderator. The moderator currently is Irene López. Make sure to be using an easily identifiable name in the online session's waiting room.
• The colloquium starts with an introduction to the agenda and the moderator asks the speaker's advisor/host to put the talk into context.
• Your talk starts. The scheduled time for your talk is normally 20min with additional 5-10min for discussion.
• The moderator keeps track of the time and will signal 2min before the end of time (e.g. by turning on their video).
• During the discussion session, the audience can ask questions, which are meant for clarification or for putting the talk into context. The audience can also ask questions in the chat.
• Congratulations! Your talk is over and it's now time to celebrate! Have you already tried the parabolic slides that bring you from the third floor to the Magistrale?

Do you remember a talk that made you feel very happy for attending? Do you also remember a talk that confused you? What made these two experiences different?

Here are a few things to check if you want to improve your presentation:

• What is the main idea that you want people to remember after your presentation? Do you make it crystal-clear? How quickly are you arriving to it?
• Which aspects of your work can you cover in the given time frame, with a reasonable pace and good depth?
• What can you leave out (but maybe have as back-up slides) to not confuse or overwhelm the audience?
• How are you investing the crucial first two minutes of your presentation?
• How much content do you have on your slides? Is all of it important? Will the audience know which part of a slide to look at? Will somebody from the last row be able to read the content? Will somebody with limited experience in your field have time to understand what is going on?
• Are the figures clear? Are you explaining the axes or any other features clearly?

In any case, make sure to start preparing your talk early enough so that you can potentially discuss it, rehearse it, and improve it.

Here are a few good videos to find out more:

Did you know that the TUM English Writing Center can also help you with writing good slides?

## Work with us!

Do your thesis/student project in Informatics / Mathematics / Physics: Student Projects at the SCCS.