MathGroup Archive 2008

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

Search the Archive

Re: Recognising parameters in function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg94563] Re: [mg94523] Recognising parameters in function
  • From: Patrick Scheibe <pscheibe at trm.uni-leipzig.de>
  • Date: Tue, 16 Dec 2008 02:36:02 -0500 (EST)
  • References: <200812151247.HAA26383@smc.vnet.net>

Hi,

because the line f[vars1]/.optim[[2]] isn't working like you expect it.
f[vars1] is evaluated to f[{x,y}] and not more because {x,y} is not a
Numeric vector!
Replacing now the x and y with the values in optim[[2]] gives f[{5,3}]
and makes it to a numeric vector which is then evaluated to z/2.
If you want to fill in your values you can write

f[vars1] /. optim[[2]] /. optim[[2]]

which is definitely not intuitive. Can you explain why you are using a
function which ignores the value of its parameters? Your function f is
similar to

g[_?(VectorQ[#, NumericQ] &)] := 1/2 (x - 5)^2 + (y - 3)^2;

I really don't see the reason for that. If you can tell that, I can
explain why the FindMinimum-line works.

Cheers
Patrick



On Mon, 2008-12-15 at 07:47 -0500, Stuart Nettleton wrote:
> Hi, would someone be able to suggest why FindMinimum will recognise  
> parameters in the following function but the backsubstitution will not.  
> Thanks for any help, Stuart
> Clear[f, vars1, z];
> vars1 = {x, y};
> z = (x - 5)^2 + (y - 3)^2;
> f[vars_] := Module[{a},
>      a = z/2;
>      Return[a]
>      ] /; VectorQ[vars, NumericQ];
> optim = FindMinimum[Join[{f[vars1]}, Thread[vars1 >= 0]], vars1]
> optim[[2]]
> f[vars1] /. optim[[2]]
> 
> --
> UTS CRICOS Provider Code:  00099F
> DISCLAIMER: This email message and any accompanying attachments may contain
> confidential information.  If you are not the intended recipient, do not
> read, use, disseminate, distribute or copy this message or attachments.  If
> you have received this message in error, please notify the sender
> immediately and delete this message. Any views expressed in this message
> are those of the individual sender, except where the sender expressly, and
> with authority, states them to be the views the University of Technology,
> Sydney. Before opening any attachments, please check them for viruses and
> defects.
> 



  • Prev by Date: Re: Did I trash Mathematica installation?
  • Next by Date: Re: Re: branch of (-1)^(1/3)
  • Previous by thread: Recognising parameters in function
  • Next by thread: Re: Recognising parameters in function