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Re: Inverse of a six-parameter asymmetric sigmoidal curve

• To: mathgroup at smc.vnet.net
• Subject: [mg111233] Re: Inverse of a six-parameter asymmetric sigmoidal curve
• From: "J. Batista" <jbatista800 at gmail.com>
• Date: Sat, 24 Jul 2010 05:08:22 -0400 (EDT)

If I understood the statement of your problem correctly, omitting the term
k*Log[x] works merely because the mathematical expression is then no longer
implicit.  Therefore, using your original mathematical expression, it does
not look like you are going to be able to generate x = f(y) from y = f(x) in
this case.  Your original y = f(x) is an implicit function.

Regards,
J. Batista



On Fri, Jul 23, 2010 at 7:08 AM, spiceman <aspiess at uke.de> wrote:

> Hi everybody,
>
> does anybody have a clue how to get Mathematica to deliver the inverse of
> the following function?
>
> fct := c + (k * Log[x]) + (d - c)/(1 + Exp[b*(Log[x] - Log[e])])^f
> Solve[fct == y, x]
>
> Solve::tdep: The equations appear to involve the variables to be solved for
> in an essentially non-algebraic way.
>
> I suppose I have to transform somehow. Any clues?
> Omitting k*Log[x] works...
>
> Thnaks in advance,
> -ans
>
>