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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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