STE||AR Spotlight: Patrick Diehl

Patrick Diehl is a research scientist here in the STE||AR Group at CCT – LSU. He is definitely one of our most active members!  In addition to his extensive research activities and numerous publications, Patrick also teaches in the LSU Math Department and has organized several workshops and events.

Before joining LSU, Patrick was a postdoctoral fellow at the Laboratory for Multiscale Mechanics at Polytechnique Montreal. He received his diploma in computer science at the University of Stuttgart and his Ph.D. in Applied Mathematics from the university of Bonn.

Patrick created and hosted the virtual CAIRO colloquium series in the Spring.  Speakers from across the country, and even internationally, joined to discuss various AI (artificial intelligence) topics.  The series was an overall success and will continue in the Fall.

Patrick is the liaison for universities in Louisiana for the Texas and Louisiana section of the Society for Applied and Industrial Mathematics (SIAM). He is a topic editor for the Journal for Open Source Software (JOSS) for computational fracture mechanics, applied mathematics, C++, asynchronous and task-based programming.

Patrick also cohosts a podcast – FLOSS For Science – with episodes that showcase free, libre and open source software uses in science with the aim to advocate for the usage of Open Source software in academia and higher education.

Patrick’s main research interests are:

Computational engineering with the focus on peridynamic material models for the application in solids, like glassy or composite materials

High performance computing, especially the asynchronous many task system (ATM), e.g. the C++ standard library for parallelism and concurrency (HPX) for large heterogeneous computations.

In addition, Patrick has a deep interest in the usage of Open Source software to enhance the openness of Science. With respect to teaching, he is interested to develop tools to easily introduce C++ and parallel computing to non-computer science students.

Patrick lives in Baton Rouge with his wife Sylvia and their young daughter Ava.  Aside from all the great work he does at LSU, he’s an active family man and enjoys trips to the park and gymnastics lessons for Ava.  Some of their favorite activities are enjoying the local Cajun food and visiting the amazing BREC parks.

Important: IRC channel change

Because of the growing problems with Freenode we have decided to move our IRC channel to a different network. Please /join #ste||ar at Libra.Chat (irc:// If you are using the Matrix bridge to IRC, you can join #ste|| through Matrix.

HPX’s Season of Docs 2021

By Rachitt Shah

HPX was recently selected to be part of Google’s Season of Docs (GSoD), a program designed to improve the documentation of open source software, as well as being a Google Summer of Code organization.

GSoD aims to cover and create the documentation gaps faced by organizations due to various reasons, alongside giving technical writers an avenue to showcase their skills.

I will be helping in the organization and update of the prior documentation to make it into a more navigable and to provide a user-friendly structure, which many users have had issues with using the current documentation. I will work closely with the HPX team and our users to collect feedback, find user pain-points, and improve preexisting docs, which mainly comprise of the build instructions.

Alongside, I would create a “design document” containing guidelines for how to add new content to the documentation: tips on how to structure new sections, general guidelines on what sort of content should be presented in what chapters, etc. The project may also include content rearrangement and a change of hierarchy, if the users find it is needed. 

I am currently working on a timeline and action items and researching about the possible shift to another documentation platform.

I am reachable at or on the IRC as rachitt_shah, please contact me to suggest changes to the documentation or to provide feedback. We can always benefit from your ideas.

About me, I’m an undergrad studying electronics as my major, and I’m a casual sport programmer as well. I’ve been a product manager and venture capital intern in the past, and done Google Summer of Code with OpenAstronomy.

GSoC 2021 Participants Announced!

It is time to announce the participants for in the STE||AR Group’s 2021 Google Summer of Code! We are very proud to announce the names of the 2 students this year who will be funded by Google to work on projects for our group.

These recipients represent the very best of the many excellent proposals that we had to choose from. For those unfamiliar with the program, the Google Summer of Code brings together ambitious students from around the world with open source developers by giving each mentoring organization funds to hire a set number of participants. Students then write proposals, which they submit to a mentoring organization, in hopes of having their work funded.

Below are the students who will be working with the STE||AR Group this summer listed with their mentors and their proposal abstracts.


Akhil J Nair, Army Institute Of Technology ( Savitribai Phule Pune University)


Giannis Gonidelis

Hartmut Kaiser

Project: Adapting algorithms to C++ 20 and Ranges TS

I’m Akhil J Nair, a third year undergrad studying computer engineering at AIT, Pune. I’ll be working with the STE||AR group this summer, focusing on the algorithms part of HPX, working on tasks such as adapting the parallel algorithms to C++ 20, adding range overloads, sentinel overloads etc. The algorithms would be adapted to use the tag_invoke customization point mechanism and the C++ 20 overloads will be added according to the C++ 20 Standard. The ranges overloads will also be added as proposed in the C++ extensions to ranges. Adding sentinel overloads and separating the segmented algorithms for the few remaining algorithms will also be done. I’m hoping this would serve as an entry point for me to HPX and the wider world of HPC in general and I look forward to contributing and learning a lot over the coming months.


Srinivas Yadav, Keshav Memorial Institute of Technology, Hyderabad, India


Nikunj Gupta

Patrick Diehl

Project:  Add vectorization to par_unseq implementations of Parallel Algorithms

I am Srinivas Yadav currently pursuing my Bachelors in Computer Science at KMIT, Hyderabad, India. I will be working with STE | | AR group for HPX this summer in the area of vectorization for parallel algorithms. Current hpx parallel algorithms do not support vectorization. Vectorization allows the algorithms to use the cpu vector registers and hence performance may be improved by utilising most of the cpu resources and allows us to exploit another level of parallelism. This project aims to implement the support for parallel algorithms with explicit vectorization with new `simd` execution policy by using the c++ experimental simd extensions. I hope contributing to HPX would serve me as a stepping stone to the world of HPC and I am looking forward to learning and contributing more over the coming months.

Octo-Tiger Breakthrough Article

Our Octo-Tiger team here in the STE||AR Group are making waves with their newly published journal article in Monthly Notices of the Royal Astronomical Society, “Octo-Tiger: A New, 3D Hydrodynamic Code for Stellar Mergers That Uses HPX Parallelisation,”

The paper investigates the code performance and precision through benchmark testing. The authors, Dominic C. Marcello, postdoctoral researcher; Sagiv Shiber, postdoctoral researcher; Juhan Frank, professor; Geoffrey C. Clayton, professor; Patrick Diehl, research scientist; and Hartmut Kaiser, research scientist, all at LSU — together with collaborators Orsola De Marco, professor at Macquarie University and Patrick M. Motl, professor at Indiana University Kokomo — compared their results to analytic solutions, when known and other grid-based codes, such as the popular FLASH. In addition, they computed the interaction between two white dwarfs from the early mass transfer through to the merger and compared the results with past simulations of similar systems.

The LSU Physics and Astronomy press release was picked up by almost a dozen computer science and other media sites, including, and SciTechDaily.  This is an exciting breakthrough as the astrophysics code outlined in the article is able to quickly and accurately simulate the collision of stars.

Understanding stars is fundamental to understanding the smaller planets that orbit them and the large galaxies they inhabit. Stars change over million to billion-year timescales in complex ways, particularly if we consider that many of them are orbited by one or more close companions, with which they exchange mass at different stages during their lives. Recent observations of these mass exchanges as flashes of light, or “transients”, show us a fundamentally new paradigm of stellar evolution, where even well-known phenomena like supernovae need to be understood in a new light. We need to include interacting, multiple stars in our models to explain exploding, outbursting, colliding, and merging stars, to interpret the rapidly increasing number of observations of transients and to ultimately create a new model of stellar evolution.

Octo-Tiger is currently optimized to simulate the merger of well-resolved stars that can be approximated by barotropic structures, such as white dwarfs or main sequence stars. The gravity solver conserves angular momentum to machine precision, thanks to a correction algorithm. This code uses HPX parallelization, allowing the overlap of work and communication and leading to excellent scaling properties, allowing for the computation of large problems in reasonable wall-clock times.

The research outlines the current and planned areas of development aimed at tackling a number of physical phenomena connected to observations of transients.

The video by Sagiv Shriber, found here:, shows a simulation of the motion of two white dwarfs in each other’s orbits. We are looking down at these two stars as they begin to merge together.

The collaborative Octo-Tiger project continues, and we look forward to their novel and exciting work in now and in the future.

  • Octo-Tiger is funded by: National Science Foundation Award1814967
  • The following computational sources were utilzed to conduct the research: QueenBee2 at Louisiana Optical NetworkInitiative (LONI); BigRed3 at Indiana University was supported by Lilly Endowment, Inc., through its support for the Indiana University Pervasive Technology Institute; and Gadi from  the  National  Computational  Infrastructure (NCI  Australia), an NCRIS enabled capability supported by the Australian Government.

HPX accepted for Google Season of Docs 2021

This year Google is organizing the 3rd annual Google Season of Docs (GSoD). Like Google Summer of Code (GSoC) the program aims to match motivated people with interesting open source projects that are looking for volunteer contributions. GSoD, however, aims to improve open source project documentation, which often tends to get less attention than the code itself. We recognize this all too well in the HPX project. For this reason, we decided to apply for GSoD and can now proudly announce that HPX is one of 30 organizations selected to participate in this year’s GSoD!

This means that we are now looking for motivated people to help us improve our documentation. If you have some prior experience with technical writing, and are interested in working together with us on making the documentation of a cutting-edge open source C++ library the best possible guide for new and experienced users, this is your chance. You can read more about the program on the official GSoD home page. The project proposal that writers would work on can be found here. Writers are welcome to adapt aspects of the project to their specific interests. Our current documentation can be found here.

The deadline for technical writer applications is May 11 anywhere on earth. Apply here! Come talk to us about your ideas and your application on our mailing list, IRC, or Slack. We’d love to hear from you!

GSoC’21: Come and code a STE||AR Summer with us!

The STE||AR Group is honored to be selected as one of the 2021 Google Summer of Code (GSoC) mentor organizations! This program, which pays students over the summer to work on open source projects, has been a wonderful experience for students and mentors alike. This is our 7th summer being accepted by the program!

Interested students can find out more about the details of the program on GSoC’s official website. As a mentor organization we have come up with a list of suggested topics for students to work on, however, any student can write a proposal about any topic they are interested. We find that students who engage with us on IRC (#ste||ar on freenode) or via our mailing list have a better chance of having their proposals accepted and a better understanding of their project scope. Students may also read through our hints for successful proposals.

If you are interested in working with an international team of developers on the cutting edge of C++ parallel, task-based runtime systems please check us out!

HPX 1.6.0 Released!

The STE||AR Group is proud to announce the release of HPX 1.6.0! HPX is an implementation of the C++ standard library for parallelism and concurrency on an efficient user-level threading runtime, with extensions for distributed computing.

This release continues the focus on C++20 conformance with multiple new algorithms adapted to be C++20 conformant and becoming customization point objects (CPOs). We have added experimental support for HIP, allowing existing CUDA features to now be compiled with hipcc and run on AMD GPUs as well. We have also continued improving the performance of the parallel executors, and added an experimental fork-join executor. The full list of improvements, fixes, and breaking changes can be found in the release notes.

Thank you to everyone in the STE||AR Group and all the volunteers who have provided fixes, opened issues, and improved the documentation.

Download the release from our releases page.

If you have any questions, comments, or exploits to report you can reach us on IRC (#ste||ar on freenode), on the matrix hpx channel, or email us at hpx-users. We depend on your input!

HPX 1.5.1 Released!

We have just released HPX 1.5.1. This patch release fixes problems found in the 1.5.0 release. It contains the following changes:

  • Removes restriction on suspending runtime with multiple localities, users are now responsible for synchronizing work between localities before suspending.
  • Fixes several compilation problems and warnings.
  • Adds notes in the documentation explaining how to cite HPX.

Download the release from our releases page or by checking our the 1.5.1 tag. Please see our release notes for a full list of fixed issues and merged pull requests.

If you have any questions, comments, or exploits to report you can reach us on IRC (#ste||ar on freenode), on the matrix hpx channel, or email us at hpx-users. We depend on your input!

HPX 1.5.0 Released!

Make sure to read our release notes for a full list of changes as they contain important information on deprecations and breaking changes.

Thank you to everyone in the STE||AR Group and all the volunteers who have provided fixes, opened issues, and improved the documentation.

Download the release from our releases page.

The highlights of this release are:

  • We continued with the modularization. This results in the deprecation of several headers which have been moved to a different location while better matching the standard ones, we encourage you to update your includes to the new header location as soon as possible as it will be removed in a couple of releases. Here is the link to the headers you should refer to the public API.
  • We adapted several algorithms to be C++20 conformant and added hpx::stable_sort.
  • We have refactored the CMake target, you can now link directly to HPX::hpx (link additionally to HPX::wrap_main to have your main() to be used as the first HPX thread).
  • HPX now requires a C++14 compatible compiler and the standard is set by default to C++14.

If you have any questions, comments, or exploits to report you can reach us on IRC (#ste||ar on freenode), on the matrix hpx channel, or email us at hpx-users. We depend on your input!