[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Help-gsl] Strange gsl_blas_dsymv() behaviour
From: |
Frank Reininghaus |
Subject: |
Re: [Help-gsl] Strange gsl_blas_dsymv() behaviour |
Date: |
Thu, 6 Mar 2008 20:41:35 +0100 |
User-agent: |
KMail/1.9.6 (enterprise 0.20070907.709405) |
Hi,
the problem is the limited precision of 'double' operations, see
http://en.wikipedia.org/wiki/Floating_point#Accuracy_problems
The sum or product of two doubles can generally not be represented as a
double, and therefore, rounding errors occur. A consequence of this is that
the result of a summation can depend on the order in which the terms are
added, and that's what happens in your example. The relative difference
between the two results you expected to be equal is about 1e-16, and that's
in the range of rounding errors you can expect for double operations.
Frank