[Help-gsl] problem with selftest.c on x86 32-bit

[Elena Ivanova]

Dear Sir/Madam,
Could you help me with the selftest.c (see the attached file).
I've  received different results on sparc and intel for 32-b

Running the GSL self test suite I am seeing the following error when 
running
on x86 32-bit:

make[3]: Entering directory `$(@D)/linalg'
FAIL:   LQ_update m(5,3) [88]
FAIL: LQ Rank-1 Update [97]
FAIL: test
==================
1 of 1 test failed
==================

The same test works just fine on 32-bit SPARC:

make[3]: Entering directory `$(@D)/linalg'
Completed [233845/233845]
PASS: test
=============
1 test passed
=============

The test failed with the following results:

   Expected: 0                         1
   Got     : 6.82121026329696178e-13   1.00000000000056843

i.e. an absolute error in the case of 0 expected is ~ 6.8e-13 (instead 
of ~2.5e-13);   /2 * 512.0 *  2.2204460492503131e-16
a relative error in the case of 1 expected is ~ 5.7e-13  (instead of 
~2.5e-13);            /2 * 512.0 *  2.2204460492503131e-16

The implementation in the cases of sparc and intel is different, because 
of the different assembler code for sparc and intel.
Rounding also can be different.
Therefore, the absolute or relative error of the Strassen algorithm can 
be different on different platforms.
The question is, which max value of error is acceptable.
I do not understand, why the barrier value is chosen

2 * 512.0 *  2.2204460492503131e-16

2.2204460492503131e-16  is a machine eps for double.
Why 2 * 512.0 * eps?
Maybe, this is too strong condition?
The calculating error should depend on the size of source matrices.
Could you explain this to me?

Thsnk you and best wishes,
Elena Ivanova.

selftest.c
Description: Text Data