Re: Re: Square root of a square
- To: mathgroup at smc.vnet.net
- Subject: [mg107864] Re: [mg107845] Re: Square root of a square
- From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
- Date: Mon, 1 Mar 2010 04:44:07 -0500 (EST)
- References: <201002270813.DAA11868@smc.vnet.net> <201002280954.EAA25801@smc.vnet.net> <4B8B7DBF.9070200@gmail.com>
Did you not notice Adam Strzebonski's explanation in this thread?
Quote:
> It is a bug in V7.0. The function used by FullSimplify to
> simplify equations involving holonomic functions does not
> handle branch cuts correctly. It can be disabled with
>
> In[1]:= Unprotect[Holonomic`HolonomicFullSimplify];
> Clear[Holonomic`HolonomicFullSimplify];
>
> In[2]:= FullSimplify[Sqrt[x^2] == x]
>
> 2
> Out[2]= Sqrt[x ] == x
>
> Best Regards,
>
> Adam Strzebonski
> Wolfram Research
Andrzej Kozlowski
On 1 Mar 2010, at 09:41, Christoph Lhotka wrote:
> hi, this is something, which is really needed to be discussed:
>
> 1) Simplify[Sqrt[x^2] == x, x \[Element] Reals]
> 2) Simplify[Sqrt[x^2] == x, x \[Element] Complexes]
> 3) Simplify[Sqrt[x^2] == x, x < 0]
>
> works fine, while
>
> 1) FullSimplify[Sqrt[x^2] == x, x \[Element] Reals]
> 2) FullSimplify[Sqrt[x^2] == x, x \[Element] Complexes]
> 3) FullSimplify[Sqrt[x^2] == x, x < 0]
>
> will return a wrong result in the 2nd case.
>
> The problem seems to be only in version 7, not in version 6 or version =
5.
>
> chr
>
>
> Andrzej Kozlowski wrote:
>> On 27 Feb 2010, at 09:13, Mariano Su=E1rez-Alvarez wrote:
>>
>>
>>> Hi all,
>>>
>>> Mathematica evaluates FullSimplify[Sqrt[x^2]] to Sqrt[x^2], while it
>>> tells me that FullSimplify[Sqrt[x^2] == x] is True.
>>> Are these the expected answers?
>>>
>>> -- m
>>>
>>>
>>
>> The second certainly not the answer I would expect, in fact this =
looks to me like a serious (perhaps even "shocking") bug. It certainly =
contradicts this answer:
>>
>> FindInstance[Sqrt[x^2] != x, x]
>>
>> {{x -> -(109/5) + (11*I)/5}}
>>
>>
>> Andrzej Kozlowski
>>
>>
>>
>>
>> :
>