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Re: FullSimplify and negative radicands

  • To: mathgroup at smc.vnet.net
  • Subject: [mg110209] Re: FullSimplify and negative radicands
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Tue, 8 Jun 2010 07:08:19 -0400 (EDT)

It's a bug involving simplification of holonomic functions in Mathematica 7, which has already appeared a couple of times on this forum. You can avoid it by evaluating:

Unprotect[Holonomic`HolonomicFullSimplify];
Clear[Holonomic`HolonomicFullSimplify];

Andrzej Kozlowski



On 7 Jun 2010, at 21:23, Torsten Schoenfeld wrote:

> Why does FullSimplify think this equation is true even though x == -3 is
> clearly a counterexample?
>
> In[1]:== equation == Sqrt[x^2 - 1] ==== Sqrt[x + 1] Sqrt[x - 1]
> Out[1]== Sqrt[-1 + x^2] ==== Sqrt[-1 + x] Sqrt[1 + x]
>
> In[2]:== $Assumptions
> Out[2]== True
>
> In[3]:== equation // FullSimplify
> Out[3]== True
>
> In[4]:== equation /. x -> -3
> Out[4]== False
>
> (This is with Mathematica 7.0.1.0.)
>


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