Cactus Workshop - NCSA Sep 27 - Oct Scott H. Hawley*, Matthew W. Choptuik*  *University of Texas at Austin *  University of British Columbia Toward Automatic Parallel Adaptive Mesh Refinement Credits: Manish Parashar, James C. Browne, Paul Walker, Shyamal Mitra, Robert Marsa, Mijan Huq, Dae-Il Choi

When we model physical phenomena using finite-difference approximations of partial differential equations… n For fixed local accuracy, required resolution may vary widely in space and time n Resolution requirements may not be known a priori  Adaptive Mesh Refinement (AMR) Even with the utility AMR provides, a code must be parallelizable to take advantage of modern computing machinery Motivation

Motivation, cont’d n AMR and parallel processing are desirable, but both present challenges which may be prohibitive for many researchers  Investigate environments in which AMR and parallelism are provided automatically

Paradigm n Almost all details of AMR and parallelism hidden from user l Provide unigrid routines l Specify –maximum # of levels – truncation error tolerance for regridding –clustering efficiency l Entire AMR driver generated automatically n User selects “AMR: On” (someday soon)

GrACE provides structures for AMR and parallelization Goal: Make GrACE features easily accessible to end user Provide: l Generic Driver (“Your code here”) l Output support l Supplemental Documentation (“How to…”) l Link to RNPL Build Around GrACE

Rapid Numerical Prototyping Language (RNPL) n Minimal development time l Specify: –Initial Data –Boundary Conditions –Finite Difference Equations n Examples: l Pedagogy: Scalar wave in IEF coordinates l Boson star simulations l Generate framework for fluid codes n Easily used to write Cactus Thorns Marsa & Choptuik

Coincident Goals Both this effort and Cactus seek automatic, parallel AMR in the very near future n Cactus needs to deliver AMR l Generic GrACE driver could be run as a Cactus Thorn –Maybe “The” Cactus AMR Thorn n Problems my group want to solve l My dissertation: Accretion disk theory within IMSO (Scott needs to land a job…) l Others: Gamma-ray burst models, Multi-D critical phenomena, and much more! David Neilsen, Jason Ventrella, Ethan Honda, Scott Noble l Cactus better connected with a wide variety of computing support than we can provide on our own

Needs n Visualization of AMR data l Interactive tool for daily use –Not necessarily “flashy” or “high-performance” l Inexpensive l Curvilinear coordinate systems l Animation l Grid-grid operations (+,-,*,/,etc) l Easy for user to add new functionality (filters, parameters) n Efficient Collaboration l Daily is not interactive enough to achieve short turn-around