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Tom_C_2
Beginner
42 Views

MKL giving different results for different argument alignments

We're seeing DSYEVX in MKL give different results when the A matrix is aligned on a 16-byte boundary or not.  A very simple test case is available at https://github.com/tomkcook/dsyevx_bug.

We're using the following product versions:

  • Microsoft Visual Studio 2013 Version 12.0.40629.00 Update 5
  • Intel(R) Visual Fortran Composer XE 2013 SP1 Update 2 Integration for Microsoft Visual Studio* 2013, 14.0.0086.12
  • MKL 11.1 Update 2

We've got some more info on this, but before I waste anyone's time with that, I'd appreciate if someone could confirm this is actually a bug an not just me doing something daft!

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4 Replies
mecej4
Black Belt
42 Views

The source file at Github has several lines with over 300 characters. Many compilers cannot handle more than 132 characters per line.

Tom_C_2
Beginner
42 Views

Thanks for the comment, but I'm fairly confident that's not what's happening here.  Even if the lines were being silently truncated, that should cause a compile error as the line-continuation ampersands are at the ends of lines.

TimP
Black Belt
42 Views

Check the discussions on  this subject on the MKL forum, and consider whether you want to try the conditional numerical reproducibility options.

If you wish to minimize alignment dependencies in your own compiled code, set -fp:source or equivalent VS property.

Aligned results may be slightly more accurate, with differences indicative of the level of accuracy.

Gennady_F_Intel
Moderator
42 Views

Tom, Could you check the problem with the latest version of MKL 11.3?  This version fully supports unaligned input. But, please take into account - the #of threads should be the same from run to run.

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