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Re: inconsistency with Inequality testing and Floor

  • To: mathgroup at smc.vnet.net
  • Subject: [mg59959] Re: inconsistency with Inequality testing and Floor
  • From: "James Gilmore" <james.gilmore at yale.edu>
  • Date: Fri, 26 Aug 2005 04:53:58 -0400 (EDT)
  • Organization: Yale University
  • References: <dek8a1$aao$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi Brett,

Convert the output of

> In[1]:=   x = 1.0 - 10^-($MachinePrecision)

to INPUT FORM. You will notice that it is not 1 and therefore there is no 
inconsistency. This is a result of rounding in Output form.

I hope all is well at UWA. Go Dockers!

-- 
James Gilmore

Graduate Student
Department of Physics
Yale University
New Haven, CT 06520 USA

"Brett Patterson" <muckle.moose at gmail.com> wrote in message 
news:dek8a1$aao$1 at smc.vnet.net...
>
> I have observed the following strange behaviour:
>
> ----------------------
> In[1]:=   x = 1.0 - 10^-($MachinePrecision)
>
> Out[1]=   1.
>
> In[2]:=   x >= 1
>
> Out[2]=   True
>
> In[3]:=   Floor[x]
>
> Out[3]=   0
> ----------------------
>
> It seems that the inequality test and Floor use different numerical
> methods.
> I think this behaviour is inconsistent.
> If the test "x >= 1" evaluates to True, then Floor[x] should evaluate
> to 1.
>
> Can anyone shed any light on this?
>
> Regards,
> Brett Patterson
>
> School of Physics, University of Western Australia; and
> Institute of Photonics, University of Strathclyde, Scotland
> 



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