Gravitational Waves Fun: Winter 2003

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