MathGroup Archive 2008

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

Search the Archive

Re: Re: "Assuming"

Mariano Suárez-Alvarez wrote:
> On Feb 23, 7:34 am, Daniel Lichtblau <d... at> wrote:
> [...]

>>[From David Cantrell:]
>>>>[...] But I do know of a case where
>>>>Mathematica goes even further, removing a singularity at which the
>>>>is defined as a number:
>>>>In[17]:= FullSimplify[UnitStep[-x^2]]
>>>>Out[17]= 0
>>>>despite the fact that correctly
>>>>In[18]:= UnitStep[-x^2] /. x -> 0
>>>>Out[18]= 1
>>>>Perhaps the simplification above is considered a bug, perhaps not.
>>A feature, really. That is, it's wrong, but FullSimplify can make
>>mistakes on measure zero sets. We do not generally regard this
>>phenomenon as a bug, though we reconsider on case by case basis.
> How does that `measure zero' allowance work in a context
> of something like
>   Assuming[Element[x, Integers], FullSimplify[something]]
> ?
> -- m

I've seen cases where the FullSimplify[something] result differs from 
something on a finite set of integers. This motivated me several months 
ago to alter assumptions of integrality, to reality (realness? 
realhood?), in processing of Integrate.

Daniel Lichtblau
Wolfram Research

  • References:
    • Re: "Assuming"
      • From: Andrzej Kozlowski <>
    • Re: "Assuming"
      • From: "Mariano Suárez-Alvarez" <>
  • Prev by Date: Re: about scoping in modules
  • Next by Date: Re: Module and Manipulate Oddity
  • Previous by thread: Re: "Assuming"
  • Next by thread: Re: Re: Re: "Assuming"