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MathGroup Archive 2007

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Re: bad performance of Reduce (5.2)

  • To: mathgroup at smc.vnet.net
  • Subject: [mg78089] Re: bad performance of Reduce (5.2)
  • From: m.r at inbox.ru
  • Date: Fri, 22 Jun 2007 06:50:06 -0400 (EDT)
  • References: <200706160734.DAA26018@smc.vnet.net>

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



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