Programming Guide¶
Note
Please consider that this project is under active development and our documentation is a work in progress.
It seems apparent that a new implementation of SDM is required; capable of modelling warm rain in LES with realistic boundary conditions and large scale forcings, and capable of application in large regional domains, with horizontal extents O(100km). CLEO is an attempt to build such a SDM. It strives to be a library for SDM to model warm clouds with exceptional computational performance.
Memory Layout¶
The fundamental basis for computational performance in CLEO is through efficient memory access patterns. Primarily this is acheived by ensuring super-droplets which occupy the same gridbox are always located contiguously in memory. We also try to avoid new memory allocation and cache misses through our organisation of gridboxes and super-droplets and we use simplistic microphysics for low cost at run-time.
Monoids¶
A key novel feature of CLEO is the construction of monoids. We use C++20 concepts to constrain templated types for microphysics and observers. This ensures they satisfy monoid set properties and can be combined in well-defined ways. The purpose is to allow for several microphysics processes (and likewise observers) to be combined simply and flexibly whilst ensuring adaptive-timestepping and avoiding the use of conditional branches in the code. This enables extra-ordinary model flexibility without additional run-time cost. It also helps with maintaining readable and modifyable code.
Coupling to Dynamics¶
Whilst CLEO handles the transport of super-droplets throughout the domain, it cannot perform advection of Gridboxes’ dyanmic variables itself (temperature, pressure, winds etc.). Instead, CLEO can be one-way or two-way coupled to a dyanmical core capable of advection. Nevertheless, such a dynamical core is not a necessity. There are many ways for CLEO to receive dynamics, which may even just involve reading data from binary files.
Kokkos Thread Parallelism¶
For performance portable thread parallelism we embrace Kokkos. As a consequence, Kokkos’ macros and functions are littered throughout our code and many of our key data structures, for example Gridboxes and super-droplets, are contained within Kokkos Views. For those seeking advanced understanding, we defer to Kokkos’ GitHub repositories and documentation therein.
Timestepping¶
As mentioned above, CLEO’s monoidal structures are designed to allow adaptive-timestepping, meaning different microphysical processes and observers may have arbitrary time-steps which bare no relation to one another and can in general change during run-time. This flexibility is contained in a sub-timestepping routine which is part of CLEO’s larger timestepping routine to run SDM coupled to dynamics.
Questions?¶
Yes please! Simply contact us!