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Re: Numerical solution from Module

  • To: mathgroup at smc.vnet.net
  • Subject: [mg132711] Re: Numerical solution from Module
  • From: Bob Hanlon <hanlonr357 at gmail.com>
  • Date: Mon, 12 May 2014 00:42:03 -0400 (EDT)
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  • References: <20140509060707.C211C6AE5@smc.vnet.net>

It is a scoping issue which is why the approach that uses explicit
parameters in f works. Alternatively, deconflict the symbols


Clear[a, b, c, f, soln];


f[x_] = (a*x + b)*x + c;


soln[aa_, bb_, cc_] = Module[{x},
   x /. Solve[f[x] == 0, x] /.
    {a -> aa, b -> bb, c -> cc}];



soln[a, b, c]


{(-b - Sqrt[b^2 - 4*a*c])/(2*a),
   (-b + Sqrt[b^2 - 4*a*c])/(2*a)}



soln[1, -3, 2]


{1, 2}



Bob Hanlon




On Fri, May 9, 2014 at 2:07 AM, Rob Y. H. Chai <yhchai at ucdavis.edu> wrote:

>
> Hello every one,
>
>
>
> Here is a simple question. Say I define a function
>
>
>
> In[14]:= f[x_] := a*x^2 + b*x + c
>
>
>
> Then I use Module to frame the solution of f[x] ==0
>
>
>
> In[15]:= soln[a_, b_, c_] := Module[{}, xsoln = Solve[f[x] == 0 , x]; x /.
> xsoln]
>
>
>
> When I enter numerical values for parameters a, b, and c in the module,
> f[x]
> never sees these numerical values, and returns a symbolic solution.
>
>
>
> In[11]:= soln[1, -3, 2]
>
>
>
> Out[11]= {(-b - Sqrt[b^2 - 4 a c])/(2 a), (-b + Sqrt[b^2 - 4 a c])/(2 a)}
>
>
>
> But I want the module to return a numerical solution as:
>
> {{x -> 1}, {x -> 2}}
>
>
>
> My question is: without bringing f[x] explicitly into the Module function,
> and without redefining f as f[a_,b_,c_][x] := a*x^2+b*x+c, how can I get
> the
> module to return a numerical solution?
>
>
>
> Thanks - Rob Chai
>
>
>




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