       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:=

sol

Out=
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:=

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

Out=

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

```

• Prev by Date: Groups of Symmetries of ODE
• Next by Date: Declare (comment), operators (Q)
• Previous by thread: Groups of Symmetries of ODE
• Next by thread: Re: Using substitution rules to define a function