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Re: Re: bad performance of Reduce (5.2)

• To: mathgroup at smc.vnet.net
• Subject: [mg78129] Re: [mg78089] Re: bad performance of Reduce (5.2)
• From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
• Date: Sat, 23 Jun 2007 07:16:23 -0400 (EDT)
• References: <200706160734.DAA26018@smc.vnet.net> <200706221050.GAA16630@smc.vnet.net>

On 22 Jun 2007, at 19:50, m.r at inbox.ru wrote:

> On Jun 17, 5:08 am, Andrzej Kozlowski <a... at mimuw.edu.pl> wrote:
>>
>> On second thoughts: there is probably not much point in testing the
>> condition that Reduce "assumed" numerically  because I am sure Reduce
>> had already done so, and assumed tha tit holds precisely because it
>> passed all numerical tests at its disposal. Nevertheless, I still
>> think that the user should be able to access the full condition that
>> has been assumed, for reasons that seem to me to obvious to need
>> stating.
>>
>> AndrzejKozlowski
>
> It's often convenient to set $MessagePrePrint to InputForm (or unset
> it):
>
> In[1]:= Block[{$MessagePrePrint = InputForm},
>  Reduce[Sin[ArcTan[z] + ArcTan[2*z]] == 1/Sqrt[2] && z > 0, z, Reals]]
>
> During evaluation of In[1]:= Reduce::ztest: Unable to decide whether \
> numeric quantities HoldForm[{(Pi - 4*ArcTan[(-3 + Sqrt[17])/4] - \
> 4*ArcTan[(-3 + Sqrt[17])/2])/4, (3*Pi - 4*ArcTan[(3 + Sqrt[17])/4] - \
> 4*ArcTan[(3 + Sqrt[17])/2])/4}] are equal to zero. Assuming they are.
>
> Out[1]= z == 1/4 (-3 + Sqrt[17]) || z == 1/4 (3 + Sqrt[17])
>
> Maxim Rytin
> m.r at inbox.ru
>
>


Thanks, this indeed can be very useful. Abbreviated messages have  
been a source of irritation for me for many years and somehow I never  
noticed that one could do something about it.

Andrzej Kozlowski

• References:
  • bad performance of Reduce (5.2)
    • From: dimitris <dimmechan@yahoo.com>
  • Re: bad performance of Reduce (5.2)
    • From: m.r@inbox.ru