Cactus in a nutshell '''

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Cactus in a nutshell ...

• Cactus facilitates parallel code design, it
  enables platform independent computations and
  encourages collaborative code development between
  different groups.
• Cactus was developed as a 3D parallel
  high-performance tool for Numerical Relativity
  which would allow easy development and
  maintenance especially for collaborations.
• Modular structure user code (a thorn) plugs
  into compact core code (flesh) through an
  extensible interface. Cactus allows a programmer
  to concentrate on his area of expertise.
• User friendly thorns can be written in C, C or
  Fortran 77/90, communication programming is
  optionally abstracted away from the user.
• Cactus offers access to a range of computational
  capabilities as e.g. parallel I/O, checkpoiting,
  remote steering visualization, performance
  analysis and provides easy access to many
  cutting edge software packages as Globus HDF5,
  PETSc.
• Developed, supported and expanded by the
  Albert-Einstein-Institute in collaboration with
  many other institutes and universities worldwide,
  released under GNU Opensource license.
• Information Download http//www.cactuscode.org

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Collaboration technology needed!

• A scientists view on a large scale computation
  problem

Evolution Algorithms
Initial Data
Analysis routines
(Bettter be Fortran)
Parallel would be great
Easy job submission
Large Data Output
Big mesh sizes
Scientist cannot be required to become experts in
IT technology.
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Collaboration technology needed!

• An IT experts view on a large scale computation
  problem

High-performanceparallel I/O
Code instrumentation steering
Next Gen.Highspeed Comm.Layers
Metacomputing
Load scheduling
Interactive Viz.
Programmers, use this!
IT experts cannot write the applications that
make use of their technology
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Large Scale Computations Require a mix of
Technologies and Expertise

• Scientific/Engineering ComponentsThe physics
  in the game
• Numerical Algorithm ComponentsFinite
  differences? Finite elements? Structured
  meshes?
• Different Computational Components
• Architectures and plattforms
• Parallelism (MPI, PVM, OpenMP, ???)
• parallel I/O, Data Management, Queueing Systems
• Visualization of all that comes out!
• How can experts work together effectively?
• Need a code environment that encourages
  collaborative HPC.

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Cactus glue
Cactus glue
Cactus goal is to provide a modular framework
that allows each technology to be of impact to
other unrelated fields.
Elliptic Equation Solver
AMR/FMR
Checkpointing
Interactive Steering
(High Performance-) Input/Output
Interactiv Visualisation
Parallelisation MPI/PVM/OpenMP/Shmem
Code Instrumentation / Bencharking
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Cactus glue in more detail

• Cactus Flesh (core) written in C
• User thorns (modules) grouped in arrangements,
  can be written in F77, F90, C, C, (Java)
• Thorn -- Flesh interface fixed in 3 files written
  in CCL (Cactus Configuration Language)
• interface.ccl Grid Variables, Arrays, Scalars
  (integer, real, logical, complex)
• param.ccl Parameters and their allowed
  values
• schedule.ccl Scheduling of routines, dynamic
  memory allocation
• Object orientated features (public, private,
  protected variables, inheritance) define scope
  of objects and ensure non-contaminating
  modularity.
• Flesh provides standard interfaces for
  Parallelization, Interpolation, Reduction, I/O,
  etc.
• Underlying technology can be replaced invisibly
  to the user

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How to use Cactus

• Develop thorns, according to the interface rules
• interface.ccl schedule.ccl param.ccl
• Specify calling sequence of the routines for
  different problems and algorithms (schedule.ccl)
• For a given code strip off parameter parsing /
  memory allocation / output
• At compile time
• Specify which thorns are to be compiled into
  executable.
• Redundancy allowed Multiple thorns providing the
  same functionality. E.g. different Evolutions
  systems, IO methods.
• At run time
• In the parameter file, turn on the thorns needed
  for your simulation.

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Cactus architectures environments

• Cactus applications developed on a standard
  workstation or laptop can be
• seamlesly run on a cluster or supercomputer.
• Supported architectures
• SGI Origin
• Cray T3E
• Compaq DEC Alpha
• Linux (IA32/64,PPC,NOWs)
• Windows NT
• IBM SP2
• Hitachi
• HP
• SUN Ultra
• .

Homogenous heterogenous networks What is a
supercomputer and what is not ? Computing in
a resource continuum
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Cactus, Egrid, KDI

• The European Grid Forum (Egrid) aims at the
  cooperative use of the distributed computing
  resources that are accessible via wide area
  networks.
• 18 participating organisations of the 1st Egrid
  workshop in Poznan chose to install Cactus as a
  first testbed application.

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Cactus_at_work HPC in Numerical Relativity

• SC 97 Distributed Spacetime, Intercontinental
  Metacomputing at AEI / Argonne / Garching /
  NCSA(512 node T3E calculation with live
  visualization San Jose)
• SC98 Colliding Neutron Stars across the
  Atlantic,Connecting T3Es in Berlin, Garching,
  San Diego
• SC99 Cactus used by several independent demos
  as underlying framework.
• In Fall 99