Re: loss of precision in doing file I/O

From:

"mlimber" <mlimber@gmail.com>

Newsgroups:

comp.lang.c++

Date:

2 Jun 2006 08:00:03 -0700

Message-ID:

<1149260403.109798.36270@u72g2000cwu.googlegroups.com>

giff wrote:

Hi all,

I have a doubt, I'll try to expose it to you as clearly as I can, maybe
it is not completely in topic, sorry about that.

I have a few vectors of doubles (output of some calculations) and I
check the norm and the dot product between couples of them before
storing them in a txt file, obtaining the expected results.

The vectors are orthonormal so the norm=1 and the dot product gives
something like 1.0e-18 that I suppose is quite close to zero...

When I read the vectors again from the txt file, I check the same things
and I find that the dot product is now around 1.0e-8.

Is this normal? Is there a way to avoid this loss of precision?

See this FAQ and those following:

http://www.parashift.com/c++-faq-lite/newbie.html#faq-29.16

Can you show us a *complete* but *minimal* code snippet that we can cut
and paste into our editors to try it? It may be user error.

I am programming in c++ using visual studio 6 on win2000.

Irrelevant. (If it is relevant, you're in the wrong newsgroup.)

Cheers! --M