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Re: floating point issue

  • To: mathgroup at smc.vnet.net
  • Subject: [mg86777] Re: floating point issue
  • From: Antti Penttilä@smc.vnet.net
  • Date: Thu, 20 Mar 2008 05:49:16 -0500 (EST)
  • Organization: University of Helsinki
  • References: <frt59r$sma$1@smc.vnet.net>

Hi,

It's 0 for me (WinXP 64-bit, Mathematica 6.0.2).

Antti

Chris Scullard wrote:
> Hi everyone,
> 
> I wonder if I can get some opinions on the best way to deal with this 
> precision issue I am having. I define the vectors:
> 
> K = {111.5, 10.5, 1.5}
> g={-0.7071068, 0., -0.7071068}
> 
> And I need this:
> 
> K.Cross[K, g]
> 
> to be 0 in accordance with a vector identity. The answer comes out to 
> around 1.3 x 10^(-13), which is certainly close to 0 but not close 
> enough for what I'm doing. I've tried various things like writing out 
> the cross product explicitly without using the functions but the result 
> is the same. And using N in various places doesn't seem to help either. 
> What's the standard solution for this kind of thing?
> 
> Thanks,
> Chris
> 


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