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MathGroup Archive 2001

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Re: lists w/o double brackets

  • To: mathgroup at smc.vnet.net
  • Subject: [mg31464] Re: lists w/o double brackets
  • From: "Ken Morgan" <kmorga51 at calvin.edu>
  • Date: Wed, 7 Nov 2001 05:29:47 -0500 (EST)
  • References: <9s5jmh$4lo$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Gavin,

You can get the list into the form you need by using Sequence instead of
List.  You can easily modify your output by using Apply.

In[1]:= Sequence@@{{var1,val1},{var2,val2}}

Out[1]= Sequence[{var1, val1}, {var2, val2}]

You should then be able to use this Sequence object as the argument to
FindRoot.

Ken Morgan
kmorga51 at calvin.edu



"Gavin K Brennen" <gbrennen at unm.edu> wrote in message
news:9s5jmh$4lo$1 at smc.vnet.net...
> Hello,
>
> I am using the function FindRoot with a large number of simultaneous
equations.
>
> FindRoot[eqs,initialvals]
>
> I have a function for generating the equations which works fine as a list
> input in FindRoot, however I am having difficulty creating a function for
> generating initialvals that will be accepted by FindRoot.  The problem
> seems to be that FindRoot demands a format
>
> FindRoot[{eq1,eq2,...,eqn},{var1,val1},{var2,val2},...,{varn,valn}]
>
> the variables and initial values of which must appear as a list without
> double brackets.  The function I have for generating the initial values
> always outputs the list as follows
>
>
> Input
> initialvals
> Output
> {{var1,val1},{var2,val2},...,{varn,valn}}.
>
> Note the double brackets which FindRoot will not accept.
> I have tried using
>
>   initialvals2=StringReplace[ToString[initialvals], {"{{" -> "{", "}}" ->
> "}"}]
>
> which eliminates the double brackets, however FindRoot will not accept
> stings as input for the variables and upon converting back to an
Expression
> using
>
> ToExpression[initialvals2]
>
> the double brackets return.
>
> Is there a solution to this without having to manually cut and paste the
> output of my expression for initialvals without the double brackets into
> FindRoot?
>
> Thanks much,
>
> Gavin
> gbrennen at unm.edu
>
>
>




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