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MathGroup Archive 2004

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Re: When Is Precision[ ] $MachinePrecision, And When Is It Not?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg47580] Re: When Is Precision[ ] $MachinePrecision, And When Is It Not?
  • From: drbob at bigfoot.com (Bobby R. Treat)
  • Date: Fri, 16 Apr 2004 05:21:26 -0400 (EDT)
  • References: <c5dhrd$nqp$1@smc.vnet.net> <c5gg7l$att$1@smc.vnet.net> <c5lfo0$bt2$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Look up == in Help, and you'll find:

"SameQ requires exact correspondence between expressions, except that
it considers Real numbers equal if their difference is less than the
uncertainty of either of them."

N[2/3] == 2/3
N[2/3] === 2/3
True
False

Bobby

Harold.Noffke at wpafb.af.mil (Harold Noffke) wrote in message news:<c5lfo0$bt2$1 at smc.vnet.net>...
> Bobby:
> 
> Thanks for your examples.  I thought about them, and found a very
> short one which still bothers me, because the answer is not what I
> expected ...
> 
> In[1]:= N[2/3]
> 
> Out[1]= 0.666667
> 
> In[2]:= N[2/3]==2/3
> 
> Out[2]= True
> 
> In[3]:= ?==
> lhs == rhs returns True if lhs and rhs are identical.
> 
> Regards,
> Harold


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