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Re: Re: Problem with parametric minimization

  • To: mathgroup at smc.vnet.net
  • Subject: [mg90282] Re: [mg90243] Re: [mg90186] Problem with parametric minimization
  • From: DrMajorBob <drmajorbob at att.net>
  • Date: Fri, 4 Jul 2008 03:59:03 -0400 (EDT)
  • References: <15947055.1215088335131.JavaMail.root@m08>
  • Reply-to: drmajorbob at longhorns.com

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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