small multithread errors

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Tue, 05/08/2012 - 12:27 am

To treat my data I have a matlab script written by a colleague which I translated into igor and adapted to my needs. The procedure is quite fit extensive. The result of both programs are in pretty good agreement (without surprise). To enhance the speed I use a multithreaded code. However the result obtained with igor multithreaded code is a little bit more noisy (for the same conditions as far as it is possible to manage them) as it is shown in the attached file while the "normal" gives exactly the same result as the matlab script.

To be a bit more precise: Each x point is the result of the the difference of two different datasets proceeded by the following function.

Threadsafe FUNCTION fitthematrix_realth(srcwv, tmpwv,outwv,row)
WAVE srcwv, tmpwv, outwv
variable row
variable i
        tmpwv = srcwv[row][p]
        CurveFit/N/Q/L=100000 /NTHR=1 poly 4,  tmpwv /D
        wave fit_dumper, M_Covar, W_coef, W_fitConstants, W_ParamConfidenceInterval, W_sigma
        wavestats/Q/M=1 fit_dumper
        outwv[row] = 0.0009 * V_minRowLoc
        killwaves/Z fit_dumper, M_Covar, W_coef, W_fitConstants, W_ParamConfidenceInterval, W_sigma
END


In the main function the loop which calls the fit procedure looks like, which is basically copy&pasted from the igor help files:

Variable n,actrow,nthreads= ThreadProcessorCount
Variable mt= ThreadGroupCreate(nthreads)
           
Variable ttime= stopMSTimer(-2)
for(actrow=0;actrow<DimSize(fieldwv,0);)
    for(n=0;n<nthreads;n+=1)
        ThreadStart mt,n, fitthematrix_realth(fieldwv, dumper,resultingfield,actrow)
        actrow+=1
        if( actrow >= DimSize(fieldwv,0) )
            break
        endif
    endfor
   
    do
        variable tgs= ThreadGroupWait(mt,1000)
    while( tgs != 0 )
endfor
variable dummy= ThreadGroupRelease(mt)
                   
Variable mt2= ThreadGroupCreate(nthreads)
for(actrow=0;actrow<DimSize(zfieldwave,0);)
    for(n=0;n<nthreads;n+=1)
        ThreadStart mt2,n, fitthematrix_realth(zfieldwave, dumper,resultingnofield,actrow)
        actrow+=1
        if( actrow >= DimSize(zfieldwave,0) )
            break
        endif
    endfor
   
    do
        variable tgs2= ThreadGroupWait(mt2,1000)
    while( tgs != 0 )
endfor                 
dummy= ThreadGroupRelease(mt2)


Where is my error?
ubi wrote:

Threadsafe FUNCTION fitthematrix_realth(srcwv, tmpwv,outwv,row)
WAVE srcwv, tmpwv, outwv
variable row
variable i
        tmpwv = srcwv[row][p]
        CurveFit/N/Q/L=100000 /NTHR=1 poly 4,  tmpwv /D
        wave fit_dumper, M_Covar, W_coef, W_fitConstants, W_ParamConfidenceInterval, W_sigma
        wavestats/Q/M=1 fit_dumper
        outwv[row] = 0.0009 * V_minRowLoc
        killwaves/Z fit_dumper, M_Covar, W_coef, W_fitConstants, W_ParamConfidenceInterval, W_sigma
END



- Why is tmpwv passed in as an argument? Each thread will overwrite tmpwv - its contents are undefined.
- You reference a wave called fit_dumper. I don't see one being created. Remember that all threads have their own data folder hierarchy, independent from the 'standard' Igor hierarchy.

That said, here's how I would implement it (note - I assume that your output is 1D and that there is one point for each row in the source matrix).
Threadsafe FUNCTION FitWorker(srcwv, row)
WAVE srcwv, tmpwv, outwv
variable row
variable i
       
CurveFit/N/Q/L=100000 /NTHR=1 poly 4,  srcwv[row][] /D
// do something with the results of the fit and WaveStats
return 0.0009 * V_minRowLoc
END

Function DoTheWork(srcWave)
wave srcWave

Make /O/N=(DimSize(srcWave, 0)) /D outputWave

MultiThread outputWave = FitWorker(srcWave, p)
End

May 8, 2012 at 12:44 pm - Permalink

741 wrote:


- Why is tmpwv passed in as an argument? Each thread will overwrite tmpwv - its contents are undefined.
- You reference a wave called fit_dumper. I don't see one being created. Remember that all threads have their own data folder hierarchy, independent from the 'standard' Igor hierarchy.

That said, here's how I would implement it (note - I assume that your output is 1D and that there is one point for each row in the source matrix).


Great that fixed the problem. Indeed I have to create tmpwv in the thread. However your suggestion seems to be a bit "lighter", I'll give a try.

May 9, 2012 at 02:07 pm - Permalink