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 > >