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What’s FLASH? How does FLASH do it?

What’s FLASH? How does FLASH do it?. Katherine M Riley Code Group. Overview. What is FLASH Basics of FLASH2 Architecture Basics behind a problem setup Walk away with: Enough of an idea of these concepts to be able to look at a sample setup and understand what is happening.

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What’s FLASH? How does FLASH do it?

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  1. What’s FLASH?How does FLASH do it? Katherine M Riley Code Group

  2. Overview • What is FLASH • Basics of FLASH2 Architecture • Basics behind a problem setup • Walk away with: • Enough of an idea of these concepts to be able to look at a sample setup and understand what is happening.

  3. FLASH: The Application • To simulate matter accreted onto the surfaces of compact stars, nuclear ignition of the accumulated (and possibly stellar) material, and subsequent evolution of the star’s interior, surface, and exterior. • Novae (on white dwarf surfaces) • Type 1a supernovae (in white dwarf interiors) • X-ray bursts (on neutron star surfaces)

  4. FLASH Results • Compressible reactive flow • Wide range of length of time scales • Many interacting physical processes • Only indirect validation possible for the astrophysics • Many people in collaboration Flame-vortex interactions Compressible turbulence Shocked cylinder Nova outbursts on white dwarfs Intracluster interactions Cellular detonations White Dwarf deflagration Helium burning on neutron stars Rayleigh-Taylor instability

  5. Physics Hydrodynamics PPM MHD Relativistic PPM Nuclear Physics Gravity Cosmology Particles Infrastructure Setup AMR: Paramesh Regular testing Parallel I/O hdf5, pnetcdf, Profiling Runtime and post-processing visualization What FLASH Provides

  6. A Little FLASH History BAM • FLASH0 • Paramesh2, Prometheus and EOS/Burn • FLASH1 • Smoothing out the smash • First form of module architecture & inheritance • FLASH2 • Untangle modules from each other (Grid) • dBase • Concept of levels of users • FLASH3 • Stricter interface control & module architecture • Taming the database

  7. FLASH2 Audiences FLASH Application Developer End User Application Programmer • Works on just about everything • Grid development • Data access • Architecture • Initialize setup • Boundary conditions • Basic data structure • (Might add a kernel) • Develop physics modules • Talk to grid • Module communication

  8. FLASH2 Code Basics • An application code, composed of units/modules. Particular modules are set up together to run different physics problems. • Performance, Testing, Usability, Portability • Fortran, C, Python, … • 560,000* lines of code • 75% code, 25% comment • Very portable • Scaling to 1000’s of procs * Internal Release

  9. Basic Computational Unit : Block • The adaptive grid is composed of blocks • All blocks: same dimensions • Cover different fraction of the physical domain. • Kevin Olson will talk about this more.

  10. First Look at FLASH • ‘The tar-ball’ • ‘source’ directories • modules or groups of modules • Post-processing tools, docs, setups • Setup • FLASH architecture tool • Selects and sets up these modules • Collecting variables, runtime parameters, etc

  11. Mesh Database Cosmology Driver Particles MHD IO Visualization mesh_init() mesh_guardcells() mesh_updateRef() mesh_fluxConserve() init() dBaseGetData() dBasePutData() dBaseProperty() init() init() Checkpoint_write() Checkpoint_read() init() init() advance() dBase_init() dBaseGetData() dBasePutData() dBaseProperty() init() render() Explicit mhd constant burn Gamma point_mass iso13 Helmholtz ... Unsplit PPM Poisson ... cool heat Diffuse WENO PPM Multigrid Multipole Structure of FLASHModules (not exact!) Hydro Gravity Source_terms Materials init() tstep() hydro3d() init() tstep() grav3d() init() tstep() src_terms() eos3d() eos1d() eos()

  12. What’s a FLASH Module? • FLASH basic architecture unit: Modules • Component of the FLASH code providing a particular functionality • Different combinations of modules are used for particular problem setups • Ex: driver, hydro, mesh, dBase, I/O • Fake inheritance by use of directory structure • Modules communicate • Driver • Variable Database

  13. mesh Abstract FLASH2 Module 1. Meta-data (Configuration Info) • Interface with driver and setup • Variable/parameter registration • Variable attributes • Module Requirements FLASH Component 2.Interface Wrapper • Exchange with variable database • Prep data for kernels • 3. Physics Kernel(s) • Single patch, single proc functions • written in any language • Can be sub-classed FLASH Application driver Collection of Flash2 Modules Database

  14. Module Implementations • FLASH2 Modules are directory trees • source/hydro/explicit/split/ppm • Each level might have source • Source relevant for all directories/implementations below • Preserves interfaces • Allows flexible implementations

  15. Inheritance Through Directories: Hydro An ‘empty’ hydro init, hydro, tstep are defaults on top of the directory tree. init hydro tstep Explicit Hydro/Explicit Replaces tstep Introduces ‘shock’ No hydro Implemented yet! tstep tstep shock Split Hydro/Explicit/Split hydro implemented Uses general explicit tstep Uses general shock Replaces init hydro hydro implemtation implemtation init DeltaForm

  16. The Module Config File • Declare solution variables, fluxes • Declare runtime parameters • Sets defaults • Lists required, exclusive modules • Config files are additive down the directory tree - no replacements

  17. Source Terms Materials Gravity MHD Driver Hydro Particles I/O Vis Setup Building an Application Configuration Tool (Setup) Database Mesh

  18. FLASH Setup: Implements Architecture • Python code links together needed physics and tools for a problem • object • Traverses modules to get implementations • Determines solution data storage list • Creates list of parameters from modules • Configures Makefiles properly

  19. Accessing the Mesh • Physics and tools access some scope of mesh • Database • Unifies method for module to access data out of its scope • Mesh data • Solution Data, Grid information • Runtime parameters • Mesh Interface • Wrappers to the public grid routines • initialize, guardcell, fluxconserve, updateRefinment

  20. FLASH Audiences FLASH Application End User • Solidify information so far • Modules and setup • How do they combine to make create an application? That runs? • Go through a little of that. • Initialize setup • Boundary conditions • Basic data structure • (Might add a kernel)

  21. Simple FLASH Flow Function Driver Init Evolve TimeStep Variable Database Data dBase Paramesh updateGrid ghostCellFill fluxConserve Evolve Hydro SourceTerms … UpdateGrid Mesh Hydro Prepare data for kernels SourceTerms Burn Heat Cool Ioniz… hydroBlock Burn burnBlock

  22. Pulling it All Together • Choose a problem setup • Run setup to configure that problem • Everything is in a new top-level directory • ‘object’ • Make • Run • Flash.par for runtime parameters • Defaults already set from particular modules

  23. Setups • A basic problem setup • Config file • Required physics modules • Flash.par • Default list runtime parameter configuration • Init_block • Initial conditions for the problem set block by block • Many other possible files: • Driver, Refinement algorithms, User defined boundary conditions • Any files in setup take precedence

  24. Provided Driver • New drivers • Put in setups • Welcome contributions • Provided: • Second order, state form, strang split evolve.F90 set time step hydro sourceTerms cosmology radiation particles gravity set time step (repeat physics) Mesh_updateGrid flash.F90 Initialize() Loop over timesteps evolvePhysics() timestep() output() visualize() End loop Finalize()

  25. What’s Next • Covered the basics of what FLASH can do • Now - How does it do it? • Alan Calder

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