Re: Finding the inverse of a function?
- To: mathgroup at smc.vnet.net
- Subject: [mg24210] Re: [mg24193] Finding the inverse of a function?
- From: BobHanlon at aol.com
- Date: Fri, 30 Jun 2000 01:57:38 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
In a message dated 6/28/2000 11:00:33 PM, heathw at in-tch.com writes:
>Is there some way to make Mathematica find the inverse of a user defined
>function? I read the Mathematica Book and found InverseFunction[ ] but
>it will only show the inverse of a Mathematica function. I would like to
>be able to find the inverse of polynomials.
>
f[x_] := Evaluate[Expand[
(x - 3)(2x + 4)(7x - 2)(x - 12)x(17x + 33)]]
The inverse of f is
g[y_] := (x /. NSolve[f[x] == y, x])
f /@ g[0] // Chop
{0, 0, 0, 0, 0, 0}
f /@ g[5]
{5.000000000003638, 5.000000000007276, 5.,
5.000000000000307, 4.999999999941792, 5.}
For some functions, FindRoot might work better.
Bob Hanlon