[Bug-gsl] [bug #52322] gsl_multifit_linear's output differs on 32 bit vs 64 bit linux

[Patrick Alken]

URL:
  <http://savannah.gnu.org/bugs/?52322>

                 Summary: gsl_multifit_linear's output differs on 32 bit vs 64
bit linux
                 Project: GNU Scientific Library
            Submitted by: psa
            Submitted on: Wed 01 Nov 2017 09:09:27 AM UTC
                Category: Runtime error
                Severity: 3 - Normal
        Operating System: 
                  Status: None
             Assigned to: None
             Open/Closed: Open
                 Release: 
         Discussion Lock: Any

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Details:

asulaiman4 =at= bloomberg =dot= net

Hello,

Please refer to {https://github.com/sulaimn2/gsltest/blob/master/gsltest.cpp}
for code.
Noticed weird output when I ran my library on 64 bit linux in dev, so I tried
to hunt down where the problem was.
In my library I am using gsl_multifit_linear from libgsl. I have to tried to
reproduce the problem with a simpler setup as follows.

Setup:
We have an X matrix with 26 coefficients and 151 observations. See x_matrix []
in gsltest.cpp
We also have a Y vector with 151 observations. See y_matrix [] in gsltest.cpp
We run gsl_multifit_linear on X and Y and produce a c vector as the output.
In 32 bit, the output was: 

c = [2.70409, 9.5864, -0.670502, 24.2728, 13.9393, 3.23134, 8.22729, 9.4926,
-0.213974, 6.85192, 0.215701, 7.49826, 7.22713, -3.39073, 13.5852, 17.3663,
-0.559321, -1.70083, 18.8802, 5.18303, 3.48551, 1.42608, 9.17107, 22.2,
-5.66091, 2.83766] //formatted for human readability.

In 64 bit, the output was:
c = [2.87233e+13, 2.87233e+13, 2.87233e+13, 2.87233e+13, 2.87233e+13,
2.87233e+13, 2.87233e+13, 2.87233e+13, 2.87233e+13, 2.87233e+13, 2.87233e+13,
2.87233e+13, 2.87233e+13, 2.87233e+13, -2.87233e+13, -2.87233e+13,
-2.87233e+13, -2.87233e+13, -2.87233e+13, -2.87233e+13, -2.87233e+13,
-2.87233e+13, -2.87233e+13, -2.87233e+13, -2.87233e+13, -2.87233e+13]

gsl_multifit_linear works when I had smaller test cases (with less
observations) so I tried to hunt down and see if there was a threshold. In
gsltest.cpp line 171, all outputs matched between 32 bit and 64 bit for all
number of observations until n=100. The moment n=101, the outputs started
being all garbage values for 64 bit linux. This number might just be a
coincidence but I am not sure.

Thanks and regards,
Ahmed



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File Attachments:


-------------------------------------------------------
Date: Wed 01 Nov 2017 09:09:27 AM UTC  Name: gsltest.cpp  Size: 15KiB   By:
psa

<http://savannah.gnu.org/bugs/download.php?file_id=42311>
-------------------------------------------------------
Date: Wed 01 Nov 2017 09:09:27 AM UTC  Name: README.md  Size: 2KiB   By: psa

<http://savannah.gnu.org/bugs/download.php?file_id=42312>

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