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Re: Re: Re: Reduce/Solve

  • To: mathgroup at smc.vnet.net
  • Subject: [mg50005] Re: [mg49995] Re: [mg49990] Re: Reduce/Solve
  • From: DrBob <drbob at bigfoot.com>
  • Date: Wed, 11 Aug 2004 05:53:00 -0400 (EDT)
  • References: <200408090829.EAA03580@smc.vnet.net> <200408101002.GAA19500@smc.vnet.net> <766AE111-EABF-11D8-BBFD-000A95B4967A@mimuw.edu.pl>
  • Reply-to: drbob at bigfoot.com
  • Sender: owner-wri-mathgroup at wolfram.com

Andrzej,

>> I see no reason to modify anything in it. Do you?

Since you ask...

All I did was apply the word "valiant" to your defense of Reduce; it's not a disparaging word. The paragraph you repeated below (from your second message in the thread) admitted something might be wrong, too, so of course you were right. You're almost always right, Andrzej.

This was preceded by a lengthy defense for Reduce's behavior, however, and look at this statement from your previous post in the thread:

>> In your particular case Solve produces a warning about using Inverse functions and tells you that you may not have a complete solution. That tells you exactly the reason why Reduce returns the original expression back to you.

"That tells you exactly the reason..."?

Maybe not. What do you think?

Bobby

On Tue, 10 Aug 2004 13:21:45 +0200, Andrzej Kozlowski <akoz at mimuw.edu.pl> wrote:

>
> On 10 Aug 2004, at 12:02, DrBob wrote:
>
>> *This message was transferred with a trial version of CommuniGate(tm)
>> Pro*
>> It's especially sad, coming on the heels of Andrsej's valiant DEFENSE
>> of Reduce!
>
> But I hope you also read my last paragraph:
>
> In this particular case I am not convinced that I should radically
> modify anything in my original reply, which is that Reduce returns the
> original input because it is "unsure" that it can return a complete
> solution using the methods available to it.
> However, perhaps I should "reduce" somewhat the degree of confidence in
> this assertion. There is just one thing that makes me slightly hesitant
> about it. This is the fact that Reduce usually in similar cases prints
> a statement to the effect that it could not solve the problem given to
> it using the methods available to it.
> Since this time nothing gets printed it could either mean that this
> statement is printed only in certain of this type of situations or that
> indeed the reason why only the original input was returned lies
> somewhere else.
>
>
> I see no reason to modify anything in it. Do you?
>
> Andrzej
>
>
>
>>
>> Bobby
>>
>> On Mon, 9 Aug 2004 04:29:32 -0400 (EDT), Dana DeLouis
>> <delouis at bellsouth.net> wrote:
>>
>>> Hello.  It is because of Mathematica's huge bug in variable names.
>>> Reduce
>>> often doesn't work because of this bug.  The first thing you need to
>>> try is
>>> to change the variable name.  I would first start by changing the "r"
>>> to a
>>> variable name that comes near the beginning of the alphabet, like "a"
>>> (at
>>> least something before the "d" in the equation).
>>>
>>> Taking your equation, and changing r to a:
>>>
>>> eq = J == J0*(1 + r/d)*Exp[-(r/d)] /. r -> a
>>>
>>> J == ((1 + a/d)*J0)/E^(a/d)
>>>
>>> Now it should work:
>>>
>>> tt = Reduce[eq, a]
>>>
>>> d != 0 && J == 0 &&
>>>    (J0 == 0 || a == -d) ||
>>>   C[1] ? Integers &&
>>>    J != 0 && J0 != 0 &&
>>>    d != 0 && a ==
>>>     -d - d*ProductLog[C[1],
>>>        -(J/(E*J0))]
>>>
>>> HTH
>>> Sad, isn't it!
>>>
>>> Dana
>>>
>>>
>>> "Dr A.H. Harker" <a.harker at ucl.ac.uk> wrote in message
>>> news:cetf3i$6i8$1 at smc.vnet.net...
>>>> Dear All,
>>>>          I tend to think of Reduce as a more powerful tool than
>>>> Solve,
>>>> yet with
>>>>
>>>> eq = J == J0 (1 + r/d) Exp[-r/d]
>>>> ss = Solve[eq, r]
>>>> tt = Reduce[eq, r]
>>>>
>>>>  I get useful output from Solve, but Reduce returns the expression
>>>> unevaluated. What am I missing?  Mathematica 5.0.0.0 under Windows
>>>> XP.
>>>>
>>>>        Tony
>>>>
>>>>  Dr A.H. Harker
>>>>  Director of Postgraduate Studies
>>>>  Deputy Head, Condensed Matter and Materials Physics Group
>>>>  Department of Physics and Astronomy
>>>>  University College London
>>>>  Gower Street
>>>>  LONDON
>>>>  WC1E  6BT
>>>>  (44)(0)207 679 3404
>>>>  a.harker at ucl.ac.uk
>>>>
>>>>
>>>>
>>>
>>>
>>>
>>
>>
>>
>> --
>> DrBob at bigfoot.com
>> www.eclecticdreams.net
>>
>
>
>



-- 
DrBob at bigfoot.com
www.eclecticdreams.net


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