January, 2004 LSU Capital 1 Gravitational Waves Fun: Winter 2003 Short overview of research activities at the LSU CAPITAL + A Short Cactus Tutorial Ruxandra Bondarescu, Cornell University Gregory Daues, NCSA

January, 2004 LSU Capital 2 Science Projects Numerical Relativity in Ed’s group at LSU People at LSU: Peter Diener (Assistant Prof. at LSU), Rioji Takahashi, Horst Beyer (Math Dept. at LSU), Francisco Guzman and many others. Collaborators around the world: –LSU, AEI: Frank Hermann, Denis Pollney, Thomas Radke; Mexico: Miguel Alcubierre;, UC Berkeley: John Shalf; UCSD: Mike Norman; UIUC: Paul Saylor; NCSA: John Towns, Greg; Washington University: Wai-Mo Suen; Caltech: Mihai and many others. Research Problems Black hole coalescence –Head on Collision –General Event Horizon Finder (Peter Diener) –Gravitational Waveform extraction –Formulation of Einstein Equations (Host Beyer) –Black Hole excision –Gauge conditions (how do you choose your coordinates in GR?) –Boundary Conditions

January, 2004 LSU Capital 3 Science Projects (continuation…) More Numerical Relativity in Ed’s group at LSU Boson Stars –Theoretical dark matter candidates - not yet observed –Francisco Guzman developed 3D GR evolution code –A lot of open problems: boson star collisions, wave form extraction, axisymmetric perturbations of boson stars (Greg, Jaya, Francisco,me), etc. –Studied as model for the supermassive objects at galactic centers (Francisco Guzman, Miguel Alcubierre) Brill Waves –The simplest non-trivial solution for initial data in General Relativity –When evolved Collapse to a BH (for large amplitudes) Implode, oscillate and disperse to infinity –Study of the critical solution at the boundary between these two regions

January, 2004 LSU Capital 4 Science Projects (continuation…) Relativistic hydrodynamics –Carpet (Erik Schnetter, Scott Hawley) - Fixed Mesh Refinement –Neutron star and stellar core collapse –Collapse of rotating neutron stars –Binary systems: NS+NS, NS+BH mergers Hydrodynamics (Mike Norman) –CactusZeus Zeus: widely used Eulerian hydro code Extragalactic jets, turbulent fluid flows, galaxy simulations ported into Cactus

January, 2004 LSU Capital 5 Computational Science Projects Grid Computing –Think of “the grid” = a single machine –Enable complicated scenarios: migration, task farming –More better, larger, simulations! –More effective use of human and computational resources Visualization –Movies: showed on Discovery Channel, bring BH to a general audience –Built software: LCA Vison (software tool for Adaptive Mesh Refinement Data) Mesh Refinement –Method for approaching problems with multiple scales –Fixed Mesh Refinement (FMR) - Carpet –Adaptive Mesh Refinement (AMR)

January, 2004 LSU Capital 6 Cactus Computational Toolkit The first attempt to build a common environment for the astrophysics & relativity community Widely used by many geographically distributed research groups –Numerical Relativity: AEI, Penn State, Texas, Wash U, Southampton, Riken, SISSA, Mexico, Brownsville, Cornell, and more... –Other Applications: Climate Modeling (NASA), Bio- Informatics(Chicago - Dave Angulo), Chemical Engeneering (U. Kansas), Early Universe(LBL), Astrophysics(Zeus), etc.

January, 2004 LSU Capital 7 Why use Cactus? Get a lot of stuff for free –Parallelization –Flexible and Portable –Supports both C and Fortran –Lots of examples, fairly good documentation –Output for specific visualization tools: xgraph, gnuplot, HDF5,jpegs … –Efficient Elliptic Equation Solver –checkpointing Easier to share your code and collaborate Modular –Cactus Flesh framework –Cactus Thorns contain the physics

January, 2004 LSU Capital 8 How easy is it to run the same problem? Start with a parameter file Get the code –% MakeThornList myBH.par –% GetCactus ThornList Compile In the Cactus directory run: –% gmake options=mymachine,config my_BH_Collision –% gmake my_BH_Collision Run your code –% cactus_my_BH_Collision myBH.par Can have several Cactus configurations from the same source code

January, 2004 LSU Capital 9 Writing a Cactus Thorn: What do I need to worry about? ThornList interface.ccl param.ccl schedule.ccl Documentation Testsuites Examples Sample parameter file

January, 2004 LSU Capital 10 Parts of a Cactus Thorn ThornList # arrangement/thorn # implements (inherits) [friend] {shares} ScalarFields/IVPSolver # (ADMConstraints)[ADMCoupling]{IO} ScalarFields/BosonEvolution # (IVPSolver) [ADMCoupling]{IO} CactusBase/IOUtil #IO (Cactus) []{} interface.ccl implements: IVPSolver inherits: ADMConstraints friend: ADMCoupling USES INCLUDE HEADER: Boundary.h Symmetry.h REAL ellcoeffs type = GF { Mcoeff,Ncoeff,conformal_factor } "Coefficients of the elliptic equation "

January, 2004 LSU Capital 11 Parts of a Cactus Thorn param.ccl shares: IO private: BOOLEAN use_ivpsolver "Use the IVP Solver" { }"no" STRING solver "Name of TATelliptic solver that should be used" {.* :: "must be an activated TATelliptic solver" } "TATJacobi”

January, 2004 LSU Capital 12 Parts of a Cactus Thorn schedule.ccl schedule Ricci at CCTK_INITIAL after ReadData{ LANG: C }"calculating the ricci tensor and scalar” schedule IVPSolver at CCTK_INITIAL after Ricci{ LANG: FORTRAN }”Solving the elliptic equation” schedule postIVPSolver at CCTK_INITIAL after IVPSolver{ LANG: FORTRAN }”resetting the metric"

January, 2004 LSU Capital 13 Conclusion Working with Ed and Gab From the students’ perspective: –A large group –A large number of problems being studied Never get bored –Work with a lot of people in a world wide collaboration – Travel a lot => many people know you; easier to find jobs –Publish many papers –Get to be independent Write proposals (have your own project! Based on your ideas!)