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Re: Re: Re: Problem with parametric minimization

  • To: mathgroup at smc.vnet.net
  • Subject: [mg90324] Re: [mg90282] Re: [mg90243] Re: [mg90186] Problem with parametric minimization
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Sat, 5 Jul 2008 04:53:24 -0400 (EDT)
  • References: <15947055.1215088335131.JavaMail.root@m08> <200807040759.DAA22360@smc.vnet.net>

Too late!
(At least I hope you liked the quote at the end).

Andrzej Kozlowski

On 4 Jul 2008, at 16:59, DrMajorBob wrote:

> DISREGARD; I'd forgotten that the result of Minimize is {optimal  
> function
> value, optimal x value}.
>
> Bobby
>
> On Thu, 03 Jul 2008 12:40:13 -0500, DrMajorBob <drmajorbob at att.net>  
> wrote:
>
>> Good idea, but the result is two solutions, the second of which is
>> incorrect:
>>
>> Minimize[a*x^2 + b*x + c, x]
>>
>> {\[Piecewise]c	(b==0&&a==0)||(b==0&&a>0)
>> ((-b^2+4 a c)/(4 a))	(b>0&&a>0)||(b<0&&a>0)
>> -\[Infinity]	True
>>
>> ,{x->\[Piecewise]0	(b==0&&a==0)||(b==0&&a>0)
>> -(b/(2 a))	(b>0&&a>0)||(b<0&&a>0)
>> Indeterminate	True
>>
>> }}
>>
>> Here's Minimize failing in similar (spectacular) fashion for a LINEAR
>> function:
>>
>> quadratic=a*x^2+b*x+c;
>> linear=quadratic/.a->0
>> Minimize[linear,x]
>>
>> c+b x
>>
>> {\[Piecewise]c	b==0
>> -\[Infinity]	True
>>
>> ,{x->\[Piecewise]0	b==0
>> Indeterminate	True
>>
>> }}
>>
>> The first solution is correct; the second is nonsense.
>>
>> (This is 64-bit 6.0.3 on the Mac.)
>>
>> Bobby
>>
>> On Thu, 03 Jul 2008 05:11:28 -0500, Bob Hanlon <hanlonr at cox.net>  
>> wrote:
>>
>>> Use multiply or space to have your expression represent what you
>>> intended.
>>>
>>> Minimize[a*x^2 + b*x + c, x]
>>>
>>>
>>> Bob Hanlon
>>>
>>> ---- Stephan Heckmueller <stephan.heckmueller at gmx.net> wrote:
>>>
>>> =============
>>> Hello,
>>> I have a problem with with the examples for using the
>>> Minimize function given in the documentation on wolfram.com:
>>>
>>> When trying:
>>> Minimize[ax^2+bx+c,x]
>>>
>>> I receive the following error:
>>>
>>> Minimize::objv:
>>> The objective function c+bx+ax^2 contains a nonconstant
>>> expression c independent of variables (x).
>>>
>>> Is there something wrong with the command or the
>>> documentation?
>>>
>>> Thanks.
>>>
>>>
>>>
>>>
>>>
>>
>>
>>
>
>
>
> -- 
> DrMajorBob at longhorns.com
>



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