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numerical instabilites for GPU results

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Felix
Felix on 18 May 2011
I run this code
T=randn(10000,64);
data=randn(1000,64,10);
Tg=gpuArray(T);
datag=gpuArray(data);
res=zeros(10000,1000);
resg=gpuArray(res);
for i=1:10
res=res+T*data(:,:,i)';
end
for i=1:10
resg=resg+Tg*datag(:,:,i)';
end
resg=gather(resg);
norm(res-resg,'fro')/norm(res,'fro')
where I would expect "res" (CPU comptuted) and "resg" (GPU computed) to be the same, but they are not.
I am running this on a Tesla Card, i.e.
gpuDevice
ans =
parallel.gpu.CUDADevice handle
Package: parallel.gpu
Properties:
Name: 'Tesla C1060'
Index: 1
ComputeCapability: '1.3'
SupportsDouble: 1
DriverVersion: 3.2000
MaxThreadsPerBlock: 512
MaxShmemPerBlock: 16384
MaxThreadBlockSize: [512 512 64]
MaxGridSize: [65535 65535]
SIMDWidth: 32
TotalMemory: 4.2948e+09
FreeMemory: 4.0671e+09
MultiprocessorCount: 30
ComputeMode: 'Default'
GPUOverlapsTransfers: 1
KernelExecutionTimeout: 0
CanMapHostMemory: 1
DeviceSupported: 1
DeviceSelected: 1
Methods, Events, Superclasses
  3 Comments
Gaszton
Gaszton on 19 May 2011
I runned the code on my gt425m:
ans =
2.4946e-016

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Accepted Answer

Felix
Felix on 20 May 2011
I upgraded to the latest drivers
270.41.19
, which seems to have fixed the problem.
  1 Comment
James Tursa
James Tursa on 20 May 2011
FYI, it is bad form to accept your own answer when Edric was the one that suggested updating your drivers.

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More Answers (1)

Edric Ellis
Edric Ellis on 19 May 2011
I've just run this using R2011a on Linux and Windows using C1060 cards, and in each case the final "norm" calculation gives a result of around 2e-16. So, this should work! Could you post the output of running
parallel.internal.gpu.CUDADriverVersion
and
ver distcomp
  4 Comments
Sean de Wolski
Sean de Wolski on 14 Mar 2012
Copying Felix' first post with license censored:
Here it is:
parallel.internal.gpu.CUDADriverVersion
ans =
260.19.26
ver distcomp
-------------------------------------------------------------------------------------
MATLAB Version 7.12.0.635 (R2011a)
MATLAB License Number: ############
Operating System: Linux 2.6.30.10-105.2.23.fc11.x86_64 #1 SMP Thu Feb 11 07:06:34 UTC 2010 x86_64
Java VM Version: Java 1.6.0_17-b04 with Sun Microsystems Inc. Java HotSpot(TM) 64-Bit Server VM mixed mode
-------------------------------------------------------------------------------------
Parallel Computing Toolbox Version 5.1 (R2011a)

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