Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2008

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Re: Problem with parametric minimization

  • To: mathgroup at smc.vnet.net
  • Subject: [mg90279] Re: [mg90243] Re: [mg90186] Problem with parametric minimization
  • From: DrMajorBob <drmajorbob at att.net>
  • Date: Fri, 4 Jul 2008 03:58:28 -0400 (EDT)
  • References: <15947055.1215088335131.JavaMail.root@m08>
  • Reply-to: drmajorbob at longhorns.com

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


  • Prev by Date: Re: Anomaly? or at least a surprise.
  • Next by Date: Re: Anomaly? or at least a surprise.
  • Previous by thread: Re: Problem with parametric minimization
  • Next by thread: Re: Re: Re: Problem with parametric minimization