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Problem with Interval Calculations?

• To: mathgroup at smc.vnet.net
• Subject: [mg30868] Problem with Interval Calculations?
• From: "Greg Arnold" <garnold at mbvlab.wpafb.af.mil>
• Date: Fri, 21 Sep 2001 04:04:06 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

Mathematica 4.1 gives me the following:

In[1]:=  expr=a*(1-a)
Out[1]= (1-a) a

In[2]:= expr /. a->Interval[{1,2}]
Out[2]= Interval[{-2,0}]

In[3]:= Expand[expr]
Out[3]= a - a^2

In[4]:= Expand[expr] /. a->Interval[{1,2}]
Out[4]= Interval[{-3,1}]

What gives?  Should the answer be the same?  I believe the expanded answer,
but I'm not sure expanding every problem before assigning the interval is
practical.

Thanks for any advice/insight,

Greg

• Follow-Ups:
  • Re: Problem with Interval Calculations?
    • From: Daniel Lichtblau <danl@wolfram.com>