Re: Square root of a square
- To: mathgroup at smc.vnet.net
- Subject: [mg107836] Re: Square root of a square
- From: Adam Strzebonski <adams at wolfram.com>
- Date: Sun, 28 Feb 2010 04:52:48 -0500 (EST)
- References: <201002270813.DAA11868@smc.vnet.net> <4E497595-481A-4F1F-9E33-86865698E172@mimuw.edu.pl>
- Reply-to: adams at wolfram.com
Andrzej Kozlowski wrote:
> On 27 Feb 2010, at 09:13, Mariano Suárez-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
>
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
- References:
- Square root of a square
- From: Mariano Suárez-Alvarez <mariano.suarezalvarez@gmail.com>
- Square root of a square