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Re: problems with NMinimize

  • To: mathgroup at smc.vnet.net
  • Subject: [mg109420] Re: problems with NMinimize
  • From: Ingolf Dahl <ingolf.dahl at telia.com>
  • Date: Mon, 26 Apr 2010 07:32:12 -0400 (EDT)
  • Organization: University of Gothenburg
  • References: <201004260850.EAA12376@smc.vnet.net>
  • Reply-to: <ingolf.dahl at physics.gu.se>

Best LAI,
Yes, if you followed the thread back, you see that we also have understood
that we might introduce an extra function f(a_?NumericQ,b_?NumericQ, ...),
but we (I guess I can include Alexey Popkov and Joe Hays in "we") sometimes
find that way clumsy. If we ask Mathematica to evaluate NMinimize, this
function is described to "minimizes f numerically with respect to x." But it
does not only this: it also first tries to evaluate f symbolically. I find
it reasonable that there should be a way to opt-out from this symbolic
evaluation. It would be convenient to have an option to NMinimize for this
purpose.

Ingolf Dahl
Sweden  

-----Original Message-----
From: Anh Ngoc LAI [mailto:laianhngoc at yahoo.com] 
Sent: den 26 april 2010 10:50
To: mathgroup at smc.vnet.net
Subject: [mg109420] [mg109413] Re: problems with NMinimize

Hi,

One way to solve this problem (if i understand your problem) is to define
your function so that only evaluates when its argument is numeric, as
follow:

f(a_?NumericQ,b_?NumericQ, ...) == ...

LAI.

--- On Sun, 4/25/10, Alexey Popkov <lehin.p at gmail.com> wrote:

From: Alexey Popkov <lehin.p at gmail.com>
Subject: [mg109420] [mg109413] [mg109405] Re: problems with NMinimize
To: mathgroup at smc.vnet.net
Date: Sunday, April 25, 2010, 6:25 AM


"Ingolf Dahl" <ingolf.dahl at physics.gu.se> =D1=81=D0=BE=D0=BE=D0=B1=D1=89=D0=
=B8=D0=BB/=D1=81=D0=BE=D0=BE=D0=B1=D1=89=D0=B8=D0=BB=D0=B0 =D0=B2 =D0=BD=D0=
=BE=D0=B2=D0=BE=D1=81=D1=82=D1=8F=D1=85
=D1=81=D0=BB=D0=B5=D0=B4=D1=83=D1=8E=D1=89=D0=B5=D0=B5: news:hqu8ai$rol$1@s=
mc.vnet.net...
> Is there any serious Mathematica user in this forum, which has not
> stumbled
> on this problem one or several times, when NMinimize, or some other
> function, tries to evaluate a numeric function symbolically first, before
> inserting the numbers? Sometimes it would be nice to have an option,
> SymbolicEvaluation->False, which could be set for NMinimize in these
> cases.
> It is not always so convenient to have to define an extra function just to
> take care of this. I think there is a whole group of commands acting
> similarly to NMinimize.
>
> Ingolf Dahl
> Sweden

I totally agree with you. I do not see anything reasonable in that obviously
numerical function (for example, NMinimize, FindMinimum, etc.) is trying for
some reason to perform symbolic computation.



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