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Numerical solution from Module

  • To: mathgroup at smc.vnet.net
  • Subject: [mg132706] Numerical solution from Module
  • From: "Rob Y. H. Chai" <yhchai at ucdavis.edu>
  • Date: Fri, 9 May 2014 02:07:07 -0400 (EDT)
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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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