Monte%20Carlo%20Instrument%20Simulation%20Activity%20at%20ISIS

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Monte Carlo Instrument Simulation Activity at ISIS
Dickon Champion, ISIS Facility
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HET Fermi Chopper Simulation
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OSIRIS Back Scattering Instrument
m2 (10cmx10cm)
m3.0 (2cmx4cm)
L1
L2
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Wish Diffractometer Guide
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Polarizing Mirror Component
Single bounce
0.4
1.2
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Double bounce
0.4
1.2
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New Vitess Module for ISIS
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Distributed Monte Carlo Instrument Simulations
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Introduction

• What is Distributed Computing
• The software we use
• VITESS Specifics
• McStas Specifics
• Conclusions

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What do I mean by Distributed Grid?

• A way of speeding up large, compute intensive
  tasks
• Break large jobs into smaller chunks
• Send these chunks out to (distributed) machines
• Distributed machines do the work
• Collate and merge the results

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Spare Cycles Concept

• Typical PC usage is about 10
• Most PCs not used at all after 5pm
• Even with heavily used (Outlook, Word, IE)
  PCs, the CPU is still grossly underutilised
• Everyone wants a fast PC!
• Can we use (steal?) their unused CPU cycles?
• SETI_at_home, World Community Grid
  (www.worldcommunitygrid.org)

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Visual Introduction to the Grid
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Suitable / Unsuitable Applications

• CPU Intensive
• Low to moderate memory use
• Not too much file output
• Coarse grained
• Command line / batch driven
• Licensing issues?

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Monte Carlo Speed-up Ideas

• Two scenarios
• Single large simulation run
• Split the neutrons into smaller numbers and
  execute separately
• Merge results in some way
• Many smaller runs
• Parameter scan

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VITESS Splitting It

• Easy mode of operation fixed executables data
  files
• Executables held on server
• Split command line into bits divide Ncount
• Vary the random seed
• Create data packages
• Upload data packages

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VITESS Running It

• Use GUI to create instrument Save As Command
• Parameter directory set to .

• Submit program parses bat file
• Substitutes V and P
• Removes header and footer
• Creates many new bat files with different --Zs
  and

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C\My_GRID\VITESSE\VITESSE\buildgtVitess-Submit.exe
example_job example.bat req_files 20 logging in
to https//bruce.nd.rl.ac.uk18443/mgsi/rpc_soap.f
cgi as tom.... Adding Vitesse dataset.... Adding
Vitesse datas.... 3e007 neutrons split into 20
chunks, of -n1500000 neutrons Total number of
Vitesse 'runs' 20 Uploading data for run
1... Uploading data for run 2... . . Uploading
data for run 19... Uploading data for run
20... Adding Vitesse datas to system.... Adding
job.... Adding jobstep.... Turning on automatic
workunit generation.... Closing jobstep.... All
done Your job_id is 4878
VITESS Running It

• Submit program creates many bat files

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VITESS Merging It

• Download the chunks
• Merge Data files
• DetectedNeutrons.dat concatenate
• vpipes trajectories count rate
• Two classes of files
• 1D - Values sum divide by num chunks-
• - Errors square, sum and divide
• 2D Sum / num of chunks

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VITESS Advantages and Problems

• Many times faster linear increase
• Needs verification runs (x3)
• Typically 11 (potentially) 30 times faster
• 12 hours runs in 1 hour!
• Very large simulations reach random limits

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VITESS Some Results
176 hours 59 hours
6hrs 20mins
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McStas Splitting It

• Different executable for every run
• Executable must be uploaded at run time
• Split n into chunks
• or run many instances (parameter scan)
• Create data ( executable) packages
• Upload packages

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McStas Running It

• Use McGui to create and compile executable
• Create input file for Submit program

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McStas Running It

• Large run
• Submit program breaks up n
• Uploads new command line data executable
• Parameter Scan
• Send each run to a separate machine

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McStas Merging It

• Many output files ? Separate merge program
• PGPLOT and Matlab implemented
• Very similar
• PGPLOT
• 1D intensities sum and divide. Errors square,
  sum and divide. Events Sum
• 2D intensities sum and divide. Errors square,
  sum and divide. Events Sum
• Matlab
• 1D Same maths, different format
• 2D Virtually the same
• Metadata leave untouched

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McStas Advantages and Problems

• Security Do we trust users?
• 100 times faster?
• Linux version much faster than Windows ?
• How do we merge certain fields?
• values '1.44156e006 10459.9 30748'
• statistics 'X03.5418 dX1.52975
  Y00.000822474 dY1.0288'
• Some issue related to randomness of moderator
  file

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Conclusions

• Both run well under Grid MP
• Submit Retrieve a few hours work
• Merge a bit more
• Needs to merge more output formats ?
• Issues with very large simulations
• More info on Grid MP at www.ud.com

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Acknowledgements

• Tom Griffin - GRID
• Ed Abel -GRID
• Stuart Ansell - MCNPX
• Mark Telling - OSIRIS
• Robert Dalgliesh - Polarization
• Laurent Chapon - WISH
• Judith Peters - HET
• Heloisa Bordallo - HET
• Geza Zsigmond -HET