Monte Carlo Instrument Simulation Activity at ISIS
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Monte Carlo Instrument Simulation Activity at ISIS. Dickon Champion, ISIS Facility. HET Fermi Chopper Simulation. OSIRIS Back Scattering Instrument. m=2 (10cmx10cm). m=3.0 (2cmx4cm). L1. L2. Wish Diffractometer Guide. Polarizing Mirror Component. Single bounce. 0.4°. 1.2°.

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OSIRIS Back Scattering Instrument

m=2 (10cmx10cm)

m=3.0 (2cmx4cm)

L1

L2



Polarizing Mirror Component

Single bounce

0.4°

1.2°


Double bounce

0.4°

1.2°




Introduction

  • What is Distributed Computing

  • The software we use

  • VITESS Specifics

  • McStas Specifics

  • Conclusions


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


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?

  • [email protected], World Community Grid (www.worldcommunitygrid.org)



Suitable / Unsuitable Applications

  • CPU Intensive

  • Low to moderate memory use

  • Not too much file output

  • Coarse grained

  • Command line / batch driven

  • Licensing issues?


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


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


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 ‘--Z’s and


C:\My_GRID\VITESSE\VITESSE\build>Vitess-Submit.exe example_job example.bat req_files 20

logging in to https://bruce.nd.rl.ac.uk:18443/mgsi/rpc_soap.fcgi as tom....

Adding Vitesse dataset....

Adding Vitesse datas....

3e+007 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


VITESS – Merging It example_job example.bat req_files 20

  • 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


VITESS – Advantages and Problems example_job example.bat req_files 20

  • 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


VITESS – Some Results example_job example.bat req_files 20

176 hours

59 hours

6hrs 20mins


McStas – Splitting It example_job example.bat req_files 20

  • 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


McStas – Running It example_job example.bat req_files 20

  • Use McGui to create and compile executable

  • Create input file for Submit program


McStas – Running It example_job example.bat req_files 20

  • Large run

    • Submit program breaks up –n#####

    • Uploads new command line + data + executable

  • Parameter Scan

    • Send each run to a separate machine


McStas – Merging It example_job example.bat req_files 20

  • 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


McStas – Advantages and Problems example_job example.bat req_files 20

  • Security: Do we trust users?

  • 100 times faster[?]

  • Linux version much faster than Windows [?]

  • How do we merge certain fields?

    • values = '1.44156e+006 10459.9 30748';

    • statistics = 'X0=3.5418; dX=1.52975; Y0=0.000822474; dY=1.0288;';

  • Some issue related to randomness of moderator file


Conclusions example_job example.bat req_files 20

  • 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


Acknowledgements example_job example.bat req_files 20

  • 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


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