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Re: solving nonlinear simultaneous equations

  • To: mathgroup at smc.vnet.net
  • Subject: [mg97998] Re: solving nonlinear simultaneous equations
  • From: "Sjoerd C. de Vries" <sjoerd.c.devries at gmail.com>
  • Date: Fri, 27 Mar 2009 05:37:29 -0500 (EST)
  • References: <gqacsu$jd9$1@smc.vnet.net> <gqd1qd$nt1$1@smc.vnet.net>

As far as I know FindRoot stops at the first answer it gets. I tried a
few starting points. The answer below is correct: just fill in these
values and you'll see they're right. There are quite probably more
correct solutions. Try filling in some other starting values.

Cheers -- Sjoerd

On Mar 26, 12:23 pm, doom... at hotmail.com wrote:
> Dear Sjoerd ,
>
> How should I decide the staring values as you gaves 0.5, 0.6, 0.4, 0.8
>
> And these results are only answers?
>
> Because in this model, answers should be t0<t1<t2<t3 basically.
>
>  {t0 -> 0.042950144337512339004069005918555574390189195213080,
>  t1 -> 0.020794416091072412934056566904308358806687991905694,
>  t2 -> 0.014356830943135308919996619330315956865348280462553,
>  t3 -> -0.29047823800632023417669910887671278352651919604465}
>
> Thanks for your reply
>
> BR.
> Dooma Casper
>
> On 3=A4=EB25=A4=E9, =A4U=A4=C86=AE=C942=A4=C0, "Sjo=
erd C. de Vries" <sjoerd=
> .c.devr... at gmail.com>
> wrote:
>
> > My guess is that you have been playing with StandardForm and
> > TarditionalForm formatting. Parts of the expressions like t1(1 - t0)
> > are internally represented as t1[1 - t0], i.e. t1 is the name of a
> > function. You can see that if you change the format to InputForm
> > (using the Cell/Convert tomenu). So, what you must do is change the
> > square brackets in parenthesis using Finf and Replace.
>
> > Additionally, the syntax of your FindRoot is wrong. You cannot have to
> > starting values. If you rfepaired that and you tweak the starting
> > values and WorkingPrecision somewhat you get:
>
> > FindRoot[{eq0, eq1, eq2, eq3},
> >  {{t0, 0.5}, {t1, 0.6}, {t2, 0.4}, {t3, 0.8}}, WorkingPrecision -> 50=
]
>
> > {t0 -> 0.042950144337512339004069005918555574390189195213080,
> >  t1 -> 0.020794416091072412934056566904308358806687991905694,
> >  t2 -> 0.014356830943135308919996619330315956865348280462553,
> >  t3 -> -0.29047823800632023417669910887671278352651919604465}
>
> > Cheers -- Sjoerd
> > On Mar 24, 12:33 pm, doom... at hotmail.com wrote:
>
> > > I'm using mathematica5.2 to solving 4 complex nonlinear simultaneous
> > > equations
>
> > > I'm only need to know the approximate answers,but "FindRoot" keeps
> > > showing "FindRoot::nlnum" error messages.
>
> > > How can I solve this problem?
>
> > > I provides my final_2.nb file by website link.
>
> > >http://awin.cs.ccu.edu.tw/~dooma/final_2.nb-=C1=F4=C2=C3=B3Q=
=A4=DE=A5=
> =CE=A4=E5=A6r -
>
> > - =C5=E3=A5=DC=B3Q=A4=DE=A5=CE=A4=E5=A6r -



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