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MathGroup Archive 2001

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Re: lists w/o double brackets

  • To: mathgroup at smc.vnet.net
  • Subject: [mg31466] Re: lists w/o double brackets
  • From: bghiggins at ucdavis.edu (Brian Higgins)
  • Date: Wed, 7 Nov 2001 05:29:53 -0500 (EST)
  • References: <9s5jmh$4lo$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Gavin,

This will do the task:

In[3]:=alist = {{x, x0}, {y, y0}};

In[4]:=Apply[f[eqns, ##] &, alist]

Out[4]=f[eqns, {x, x0}, {y, y0}]

For your application replace "f" in the above with FindRoot.

Cheers,

Brian


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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