On Apr 23, 2011, at 9:54 PM, Michael D. Berger wrote:
> On my CentOS 5 box, in a C++ program that does much arithmetic,
> including numerous matrix multiplications, I have a situation in
> in which the result depends on the nature of nearby I/O. Thus,
> with all arithmetic done with type double, and where values
> are mostly in the range [-1.0e0,+1.0e0] or nearby, I do:
>
> cerr << "some stuff" << endl;
> mat3 = matmult(mat1,mat2);
>
> I get a difference of the order 1.0e-15 depending on whether the
> cerr line does or does not end in "endl" as shown.
>
> I am imagining that there is some "randomness" in the roundoff
> that depends on the I/O situation. Is this credible? Any other
> suggestions?
>
> Thanks for your help,
> Mike.
Mike, I think I'm understanding your problem. This just sounds like a floating
point rounding issue.
You've read the floating point bible already?
http://download.oracle.com/docs/cd/E19957-01/806-3568/ncg_goldberg.html
Todd
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