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MathGroup Archive 1994

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Using substitution rules to define a function

  • To: mathgroup at yoda.physics.unc.edu
  • Subject: Using substitution rules to define a function
  • From: Jean.Peccoud at imag.fr (Jean Peccoud)
  • Date: Mon, 28 Mar 1994 16:33:11 +0200

Dear Mathgroup,

could anybody explain me what happens here ?
Sol is a solution of an equation

In[32]:=

sol

Out[32]=
                2                           2
       2 a + b w  + Sqrt[b] w Sqrt[4 a + b w ]
{{x -> ---------------------------------------}, 
                          2
 
                 2                           2
        2 a + b w  - Sqrt[b] w Sqrt[4 a + b w ]
  {x -> ---------------------------------------}}
                           2

Here I want to define a function of w which returns the first solution.

In[34]:=

invf1[w_]:=sol[[1,1,2]]
invf1[x]

Out[34]=

         2                           2
2 a + b w  + Sqrt[b] w Sqrt[4 a + b w ]
---------------------------------------
                   2

but when I want to compute the value of this function for x, w remains. 
There must be a basic trick that I did not undestand well in using rules or
patterns.
Thank you.




-----------------------------------
Jean Peccoud                                        
TIMC-IMAG                                          
Faculte de medecine de Grenoble         
F-38700 La Tronche
France

tel : (33) 76 63 71 85
fax : (33) 76 51 86 67
E-mail : Jean.Peccoud at imag.fr







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