The field of scientific computing is based on modeling various physical phenomena. A promising approach to improve the quality of this modeling is to combine highly specialized simulation tools and is common practice in fields like computational fluid dynamics (CFD). In short, important tasks are to couple simulations which model relevant phenomena on a different physical level, thus performing multiphysics computations. Although several multiphysics tools are publicly available, the implementations are typically based on assumptions with respect to the field of application. For example, a specific discretization method is used, such as the Finite Element Methods (FEMs) utilized by the Elmer framework. Aside from combining different simulators to perform multiphysics simulations, decoupling a simulation into smaller parts is of high interest. The ability to reuse these parts for different simulation setups significantly increases reusability and thus reduces long-term implementation efforts.  

The available frameworks applied in the field of distributed high-performance scientific computing usually focus on the data parallel approach based on the MPI. Typically, a mesh datastructure representing the simulation domain is distributed, thus the solution is locally evaluated on the individual subdomains. This approach is referred to as domain decomposition, and is reflected by a data parallel approach. As such, the tasks to be executed by the framework are typically processed in a sequence, whereas each plugin itself utilizes the MPI to distribute the work among the compute units, for example, to utilize an MPI-based linear solver.

ViennaX does not restrict itself to such an execution behavior, in fact its focus is on providing an extendible set of different schedulers to not only support data parallel approaches, but also serial and task parallel implementations. In this context, serial execution refers to the execution of the tasks on a shared-memory machine, enabling to execute the tasks sequentially, however, the plugins can indeed have parallelized implementations based on, for example, OpenMP or CUDA. Such an approach becomes more and more important, due to the broad availability of multi-core CPUs by simultaneously stagnating clock frequencies. On the contrary, task parallel approaches can be used to parallelize data flow applications, for instance, wave front or digital logic simulations.

ViennaX facilitates the setup of flexible scientific simulations by providing an
execution framework for plugins. The decoupling of simulations into separate components is facilitated by the framework's plugin system. Functionality is implemented in plugins, supporting data dependencies. Most importantly, the plugin system enables a high degree of flexibility, as exchanging individual components of a simulation is reduced to switching plugins by altering the framework's configuration data. Consequently, no changes in the simulation's implementation must be performed, thus avoiding recompilation and knowledge of the code base. Furthermore, decoupling simulation components into plugins also increases the reusability significantly. For example, a file reader plugin for a specific file format can be utilized in different simulations. Ultimately, the effort of changing parts of the simulation is greatly reduced, strongly favoring long-term flexibility and reusability.