[Bug-gsl] [bug #52127] Difference between 32- vs. 64-bit versions of gsl_eigen_nonsymm

[Bob Smith]

URL:
  <http://savannah.gnu.org/bugs/?52127>

                 Summary: Difference between 32- vs. 64-bit versions of
gsl_eigen_nonsymm
                 Project: GNU Scientific Library
            Submitted by: sudleyplace
            Submitted on: Wed 27 Sep 2017 09:02:40 PM UTC
                Category: Accuracy problem
                Severity: 3 - Normal
        Operating System: Windows 10 Pro (64-bit)
                  Status: None
             Assigned to: None
             Open/Closed: Open
                 Release: 2.4
         Discussion Lock: Any

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Details:

I have encountered a difference in the result of gsl_eigen_nonsymm as a 32-
vs. 64-bit executable.  The program is attached.  What am I doing wrong?

GSL Version:    2.4
Hardware:       AMD FX-8350 CPU, AUSTek Sabertooth 990FX R2.0
OS:             Windows 10 Pro (64-bit)
Description:    

For the 4x4 integer-valued double-precision matrix in the source file, the
32-bit executable displays results different from the 64-bit executable.  I
think that the 64-bit results are correct, but they are both very close.

In particular, the results differ in the both real and imaginary parts of the
resulting Eigenvalues.  For example, the 32-bit version returns the real parts
of the four Eigenvalues as

0.9999999999999996
0.9999999999999996
1.0000000000000009
1.0000000000000009

whereas the 64-bit version returns the real parts as all exactly 1.  The
differences between the 32- and 64-bit results for both real and imaginary
parts are all in the low-order three bits of the hexadecimal form of the
double-precision result.

See the comments in the attached source file for the hexadecimal displays of
the real and imaginary parts.



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File Attachments:


-------------------------------------------------------
Date: Wed 27 Sep 2017 09:02:40 PM UTC  Name: nonsymm.c  Size: 6KiB   By:
sudleyplace

<http://savannah.gnu.org/bugs/download.php?file_id=41904>

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