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[Octave-bug-tracker] [bug #51963] test normpdf fails after __opengl_info


From: Dan Sebald
Subject: [Octave-bug-tracker] [bug #51963] test normpdf fails after __opengl_info__ using fltk on Intel graphics on Windows
Date: Fri, 8 Sep 2017 14:11:27 -0400 (EDT)
User-agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:54.0) Gecko/20100101 Firefox/54.0

Follow-up Comment #1, bug #51963 (project octave):

Your example error looks to be of the tolerance variety, i.e., the answer is
correct but it is numerical precision that differs:

Abs err 5.5511e-017 exceeds tol 0

Rik might have more insight as to why a tolerance of 0 works here.  I assume
that if one follows the normpdf function all the way through it will come back
to the

y = 1/sqrt(2*pi)*exp (-(x-1).^2/2)

formula.  However, it's odd that after you launch Intel graphics driver
support, then the tolerance fails.  Could it be that the Intel driver is
taking over some of the numerical library routines for exponentiation?  I.e.,
that somehow the above expression for y as an Octave command is using the
numerical library yet when the above expression is evaluated via normpdf it is
using some Intel library?

Could you try something like:


x = [-Inf 1 2 Inf];
y1 = 1/sqrt(2*pi)*exp (-(x-1).^2/2);
graphics_toolkit ("fltk");
__opengl_info__ ();
y2 = 1/sqrt(2*pi)*exp (-(x-1).^2/2);
y1 - y2


to narrow down if maybe it is the sqrt() or exp() routine that changes?  Or
any other sequence you can think of that might be useful.

It sure is odd that only FLTK causes this whereas Qt toolkit works.

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