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]]
>
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- References:
- Recognising parameters in function
- From: "Stuart Nettleton" <Stuart.Nettleton@uts.edu.au>
- Recognising parameters in function