Simulation technology for Petascale systems: concepts, numerical algorithms and software technology

Participants of the NEST Conference 2017

Building on over 20 years of experience in neuronal network simulation technology, we have taken crucial steps to prepare NEST, The Neural Simulation Tool, for brain-scale simulations on future exascale high-performance computing systems. We focused on extending NEST capabilities, based on requirements of users inside and outside the HBP, on multi-scale runtime integration with other simulation tools, on facilitating the addition of new neuron models, and, in close collaboration with colleagues from the HBP Brain Simulation Platform, on preparing network creation and communication architecture of the simulation kernel for future exascale systems. Specifically, we

  • Extended NEST to support rate models of neuronal networks, thus permitting the investigation of network dynamics on the scale of spiking neurons, the classic domain of NEST, and the more abstract scale of rate models
  • Integrated the NEST and UG4 simulators via the MUSIC library to support multi-scale simulations coupling network dynamics in NEST with detailed solutions to the 3D cable equations in UG4
  • Developed NESTML as a domain-specific language for the specification of neuron models and implemented a tool generating optimized C++ code to add neuron models specified in NESTML to the NEST simulator
  • Eliminated critical bottlenecks in the construction of brain-scale networks requiring a very large number of parallel processes
  • Analysed user requirements for connectivity generation, drafted a more flexible and powerful user interface for neuron and connection instantiation
  • Collaborated with the Brain Simulation Platform on revised data structures for connection representation and communication patterns, to allow NEST to exploit the full power of future exascale architectures
  • Systematically reviewed all new code contributions to the NEST simulator in formalised, continuous integration based review processes in collaboration with the NEST developer community

We integrated our activities closely in the NEST user community within and outside the HBP by means of

  • Systematic monitoring and follow-up of user requests and proposals through the NEST mailing list and issue tracker
  • Regular open NEST developer video conferences (every second week)
  • Personal contact with and support to key NEST users in the HBP, especially in the Human Brain Organization, Systems and Cognitive Neuroscience, and Theoretical Neuroscience Subprojects
  • Organisation of an annual NEST Conference (before the 2017 NEST User Workshop), in collaboration with the NEST Initiative, bringing together users and developers for intense exchanges of success stories, challenges and ideas

The impact of our work

  • NEST is a well-established simulation tool for large neuronal networks, with users from inside and outside the HBP
  • Newly introduced abilities, e.g. the ability to simulate rate-based models with NEST, have been received eagerly by the community and have already led to publications currently under review:
  • Code generation using NESTML has significantly reduced the burden of porting existing network models to NEST, and thus facilitates model porting efforts in Systems and Cognitive Neuroscience, as well as outside the HBP.
  • The close interaction between NESTML developers in the High Performance Analytics and Computing Platform and NESTML users in Systems and Cognitive Neuroscience has driven the development of NESTML further and ensured that NESTML addresses the needs of computational neuroscientists.