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MathGroup Archive 2004

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Max [a,-inf]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg48610] Max [a,-inf]
  • From: "Peter Pein" <petsie at arcor.de>
  • Date: Mon, 7 Jun 2004 05:33:47 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Hi group,
does the following make any sense to you?
In[1]:=
$Version
Out[1]=
"4.0 for Microsoft Windows (July 16, 1999)"
Correct :-))
In[2]:=
Simplify[Max[-Infinity, a], a \[Element] Reals]
Out[2]=
Max[a, -Infinity]
Correct but a would be more simple
In[3]:=
FullSimplify[%, a > -Infinity]
Out[3]=
Max[a, -Infinity]
Correct, but not simplified
In[4]:=
Simplify[Max[a, b], a > b]
Out[4]=
a
Perfect!

Why does Mathematica not recognise
1.) +-Infinity is not an element of the Reals
2.) assuming a>-Inf should give Max[a,-Inf.]->a

but:
-Infinity \[Element] Reals
   False

which is true
so question #1 reduces to:
1a) why is Max[-Inf., some real number] not some real number?

The same mess for Simplify[Max[a,Infinity],a \[Element] Reals], which should
give Infinity
-- 
Peter Pein, Berlin
to write to me, start the subject with [







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