MathGroup Archive 2008

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Another question on Assuming

  • To: mathgroup at
  • Subject: [mg85915] Re: [mg85866] Another question on Assuming
  • From: Andrzej Kozlowski <akoz at>
  • Date: Wed, 27 Feb 2008 04:33:27 -0500 (EST)
  • References: <>

On 26 Feb 2008, at 13:42, 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
> -- 
> Kevin J. McCann
> Research Associate Professor
> JCET/Physics
> Physics Building
> University of Maryland, Baltimore County
> 1000 Hilltop Circle
> Baltimore, MD 21250

This is not a bug but a design feature. Assuming works only with  
functions such as Simplify, Refine, Integrate, Limit etc.,  that have  
Assumptions among their options (the one exception is PowerExpand).   
You've got to use one of such functions, so, for example,  even this  
will work:

Assuming[a > 0, Limit[Sqrt[a^2], x -> b]]


However, in the case of a function like Sqrt, which does admit the  
Assumptions option (in fact, it admits no options) Assuming does  
nothing at all.

Andrzej Kozlowski

  • Prev by Date: Re: input style within a text style cell
  • Next by Date: Normalize a collection of arrays on a specific column
  • Previous by thread: Another question on Assuming
  • Next by thread: Re: Another question on Assuming