On a CentOS box with: # uname -a Linux xxxxxx 2.6.18-194.32.1.el5 #1 SMP Wed Jan 5 17:53:09 EST 2011 i686 i686 i386 GNU/Linux
# gcc --version gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-48) and using: Template Numerical Toolkit (TNT). as well as numerical software I have written, all in C++, I am doing some voluminous and complex arithmetic. On two occasions I have encountered situations in which small, irrelevant modifications of the code result in small changes in the result. In a recent example, using type double, a result that is theoretically zero, is being approximated, reasonably, by a value of -1.16e-16. When an unused matrix variable member is added to a template class not used in that part of the calculations, the result is changed to -1.05e-16, also a reasonable result, but different. When the new variable is commented out, the difference disappears. The problem does not in itself compromise the usefulness of the result, but it does compromise confidence. Thanks for any suggestions. Mike. -- Michael D. Berger m.d.ber...@ieee.org
