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MathGroup Archive 2007

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Re: Logical Expression

  • To: mathgroup at smc.vnet.net
  • Subject: [mg73442] Re: [mg73385] Logical Expression
  • From: "Chris Chiasson" <chris at chiasson.name>
  • Date: Fri, 16 Feb 2007 01:07:32 -0500 (EST)
  • References: <200702150956.EAA04579@smc.vnet.net>

The special characters in your email are garbled, which is possibly
due to improper character encoding.

Anyway, try playing with

Experimental`$SameQTolerance

and

Experimental`$EqualTolerance

, which are described in the help browser, I believe. The inequality
functions (< <= > >= ) use the SameQ tolerance, while the equality
function ( == ) uses the Equal tolerance. You can use SameQ ( === )
instead of Equal ( == ).

On 2/15/07, Martin Schoenecker <ms_usenet at gmx.de> wrote:
> Common sense tells me that the statement that "something is equal to
> zero, and unequal to zero at the same time" is a false statement:
>
> In[1]:= a == 0 && a != 0
> Out[1]= a\[Equal]0&&a=E2=89=A00
>
> In[2]:= LogicalExpand[%]
> Out[2]= False
>
> The same, in my opinion, applies to "something is equal to zero and
> greater than zero at the same time".  Why doesn't Mathematica think so,
> and how to convince it to evaluate the following?
>
> In[3]:= a == 0 && a > 0
> Out[3]= a\[Equal]0&&a>0
>
> In[4]:= LogicalExpand[%]
> Out[4]= a\[Equal]0&&a>0
>
>
> Thanks in advance,
> Martin
>
>


-- 
http://chris.chiasson.name/


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