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Inverse of a six-parameter asymmetric sigmoidal curve

• To: mathgroup at smc.vnet.net
• Subject: [mg111178] Inverse of a six-parameter asymmetric sigmoidal curve
• From: spiceman <aspiess at uke.de>
• Date: Fri, 23 Jul 2010 07:08:48 -0400 (EDT)

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