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Re: Another question on Assuming
*To*: mathgroup at smc.vnet.net
*Subject*: [mg85891] Re: Another question on Assuming
*From*: dh <dh at metrohm.ch>
*Date*: Wed, 27 Feb 2008 04:21:00 -0500 (EST)
*References*: <fq0to0$k3s$1@smc.vnet.net>
Hi Kevin,
the manual tells you that Assuming does nothing else than append the
assumptions to $Assumptions and then evaluates expr. Your expression is
Sqrt[a^2] that does not care about $Assumptions. Therefore, you need
Refine that will care.
hope this helps, Daniel
Kevin J. McCann 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 I should get a, since there is no other
> correct answer, because the assumption that a > 0 implies that it a is a
> positive real.
>
> Bug?
>
> Kevin
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