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Re: Problem with parametric minimization

  • To: mathgroup at smc.vnet.net
  • Subject: [mg90254] Re: Problem with parametric minimization
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Thu, 3 Jul 2008 06:13:32 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, UK
  • References: <g4fhkl$9gs$1@smc.vnet.net>

Stephan Heckmueller wrote:

> 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?

Starting from a fresh kernel, I do not get any error message when 
evaluating the expression you posted:

In[1]:= Minimize[ax^2 + bx + c, x]

Out[1]= {ax^2 + bx + c, {x -> 0}}

Though I strongly suspect that what you intended was the following (note 
that you must either put a space between coefficients and variables -- 
implicit multiplication -- or add a star between them, otherwise you 
just declare some variables called 'ax' and 'bx'):

In[2]:= Minimize[a*x^2 + b*x + c, x]

Out[2]= {Piecewise[{{c, (b == 0 && a == 0) || (b == 0 && a > 0)},

        2
      -b  + 4 a c
     {-----------, (b > 0 && a > 0) || (b < 0 && a > 0)}}, -Infinity],
          4 a

   {x -> Piecewise[{{0, (b == 0 && a == 0) || (b == 0 && a > 0)},

           b
       {-(---), (b > 0 && a > 0) || (b < 0 && a > 0)}}, Indeterminate]}}
          2 a

Regards,
-- Jean-Marc


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