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Re: Another question on Assuming

• To: mathgroup at smc.vnet.net
• Subject: [mg85903] Re: Another question on Assuming
• From: "David W.Cantrell" <DWCantrell at sigmaxi.net>
• Date: Wed, 27 Feb 2008 04:27:14 -0500 (EST)
• References: <fq0to0$k3s$1@smc.vnet.net>

"Kevin J. McCann" <Kevin.McCann at umbc.edu> wrote:
> The first example in the Mathematica Help on Assuming is (in part)
>
> Assuming[a > 0, Refine[Sqrt[a^2]]]
>
> which results in the answer a, as it should; however if I type instead
>
> Assuming[a > 0, Sqrt[a^2]]
>
> I get back Sqrt[a^2]],

But you didn't ask that anything be _done_ to Sqrt[a^2].

Note that we can use Simplify instead of Refine:

In[5]:= Assuming[a > 0, Simplify[Sqrt[a^2]]]

Out[5]= a

> but I should get a, since there is no other correct answer,

No. Sqrt[a^2] is correct also; it's just not as simple as you want.

David

> because the assumption that a > 0 implies that it a is a
> positive real.
>
> Bug?
>
> Kevin