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MathGroup Archive 2005

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Re: Re: problem with FindRoot

  • To: mathgroup at smc.vnet.net
  • Subject: [mg54146] Re: [mg54088] Re: problem with FindRoot
  • From: "Janos D. Pinter" <jdpinter at hfx.eastlink.ca>
  • Date: Fri, 11 Feb 2005 03:35:04 -0500 (EST)
  • References: <cud7jj$2vm$1@smc.vnet.net> <200502100746.CAA16603@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Jose,
as I said earlier, try NMinimize.




At 03:46 AM 2/10/2005, qfwfq wrote:
>Thanks Mr. Wolf,
>
>Your solution works very well. The only problem was Mathematica 5.0
>does not like your assignment. It said:
>
>function::lvset: Local variable specification spec contains expr which
>is an assignment to var; only assignments to symbols are allowed.
>
>But it has been easy to solve it.
>
>BTW, and about your last comment
> >but this won't garantee anything for your solutions.
>you're right. Sometimes, the solutions Mathematica provides to the
>simultaneous solution of the set of equations are not correct. This is
>the reason because my initial guess to FindRoot is {24}. Do you know a
>better way to solve a set of equations with lots of exponentials. I
>only know an estimation of where the solutions are.
>
>Thnaks again,
>
>Jose
>
>
>
>Wolf, Hartmut wrote:
> > >-----Original Message-----
> > >From: qfwfq [mailto:qfwfq_0 at yahoo.com]
To: mathgroup at smc.vnet.net
> > >Sent: Tuesday, February 08, 2005 11:31 AM
> > >To: mathgroup at smc.vnet.net
> > >Subject: [mg54146] [mg54088]  problem with FindRoot
> > >
> > >Hi all!
> > >
> > >I have four equations (eq1=0, ..., eq4=0) with the the four
> > >unknowns (y1, y2, y3, y4) in exponentials. I know the interval
> > >where the solutions are, and I solve this equation set by
> > >means of FindRoot by obtaining set of solutions. Then, I make
> > >a selection between the obtained results.
> > >
> > >However, I have a dependency between variables: y1<y2<y3<y4
> > >
> > >
> > >mR = Table[FindRoot[{eqn1 == 0, eqn2 == 0, eqn3 == 0, eqn4 ==
> > >0}, {y1, Random[Real, {a, b}]}, {y2, Random[Real, {a, b}]},
> > >{y3, Random[Real, {a, b}]}, {y4, Random[Real, {a, b}]}], {24}];
> > >
> > >My question is
> > >
> > >Is there any way of include the relation between y1, ..., y4
> > >in the selection of them by Random. Something like {y2,
> > >Random[Real, {y1, b}]}, {y3, Random[Real, {y2, b}]}, ...
> > >
> > >I hope I have clearly explained my problem.
> > >
> > >Thanks
> > >
> > >
> >
> > Would this be what you intended, ordered starting values?
> >
> > mR = Table[
> >       With[{{s1, s2, s3, s4} = Sort[Table[Random[Real, {a, b}],
>{4}]]},
> >         FindRoot[{eqn1 == 0, eqn2 == 0, eqn3 == 0, eqn4 == 0}, {y1,
>s1},
> > {y2,
> >             s2}, {y3, s3}, {y4, s4}]], {24}];
> >
> > but this won't garantee anything for your solutions.
> >
> > --
> > Hartmut Wolf


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