Thanks a ton for the worked out example! I had a similar problem with gfortran, and it only appeared with large array sizes (bigger than 4000x4000 as I recall). "ulimit" was no help, I assume there's a memory constraint built in somewhere. (as an aside, I once ran into a similar problem with perl - the release on linux would only allow 200MB array sizes, but the version available on a sun machine would allow GB of array sizes)
On Fri, Nov 21, 2008 at 6:36 AM, Bill Broadley <[EMAIL PROTECTED]> wrote: > Fortran isn't one of my better languages, but I did manage to tweak your > code > into something that I believe works the same and is openMP friendly. > > I put a copy at: > http://cse.ucdavis.edu/bill/OMPdemo.f > > When I used the pathscale compiler on your code it said: > "told.f", line 27: Warning: Referenced scalar variable OLD_V is SHARED by > default > "told.f", line 29: Warning: Referenced scalar variable DV is SHARED by > default > "told.f", line 31: Warning: Referenced scalar variable CONVERGED is SHARED > by > default > > I rewrote your code to get rid of those, I didn't know some of the > constants > you mentioned dy and Ly. So I just wrote my own initialization. I skipped > the boundary conditions by just restricting the start and end of the loops. > > Your code seemed to be interpolating between the current iteration (i-1 and > j-1) and the last iteration (i+1 and j+1). Not sure if that was > intentional > or not. In any case I just processed the array v into v2, then if it > didn't > converge I processed the v2 array back into v. To make each loop > independent > I made converge a 1D array which stored the sum of that row's error. Then > after each array was processed I walked the 1-d array to see if we had > converged. I exit when all pixels are below the convergence value. > > It scales rather well on a dual socket barcelona (amd quad core), my > version > iterates a 1000x1000 array with a range of values from 0-200 over 1214 > iterations to within a convergence of 0.02. > > CPUs time Scaling > ================= > 1 54.51 > 2 27.75 1.96 faster > 4 14.14 3.85 faster > 8 7.75 7.03 faster > > Hopefully my code is doing what you intended. > > Alas, with gfortran (4.3.1 or 4.3.2), I get a segmentation fault as soon as > I > run. Same if I compile with -g and run it under the debugger. I'm > probably > doing something stupid. > > -- - - - - - - - - - - - - - - - - - - - - - Nathan Moore Assistant Professor, Physics Winona State University AIM: nmoorewsu - - - - - - - - - - - - - - - - - - - - -
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