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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