Re: Help with fitting

*To*: mathgroup at smc.vnet.net*Subject*: [mg131495] Re: Help with fitting*From*: Bob Hanlon <hanlonr357 at gmail.com>*Date*: Sat, 10 Aug 2013 04:38:54 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-outx@smc.vnet.net*Delivered-to*: mathgroup-newsendx@smc.vnet.net*References*: <20130809054847.0CB036A06@smc.vnet.net>

data = {{0.1, 1400}, {0.5, 10}, {1, 5}, {5, 20}, {10, 250}}; I am guessing that this is what you intended for the equation eqn = Log [y/b] == Log [a*x/b + a*x/b] + (-0.22 + Log [a*x/b]^2) // Rationalize; expr = (y /. Solve[eqn, y][[1]])[[1]]; param = FindFit[data, expr, {a, b}, x] {a -> 1.14522, b -> 2.27658} LogLogPlot[ Evaluate[expr /. param], {x, .05, 20}, Epilog -> {Red, AbsolutePointSize[4], Point[Log[data]]}] Bob Hanlon On Fri, Aug 9, 2013 at 1:48 AM, ismail <ism45 at yahoo.com> wrote: > Hello, > > I have experimental data with (y) and (x) > > I need to fit them into the following model > > Log (y/b) = Log (ax /b/1+ax/b) + (-0.22/1+(log ax/b)^2) > > The result should be a plot with Log y on the y-axis, Log x in the x axis. > and the two constants a and b will be the result of the fitting. > > I tried that in Mathematica, but my problem is that I don't know how to > define the function so I can keep (Logy/b) in the left side. > > Mathematica allows me only to defin a model in the form (y=f(x)) > > Any help please? > >

**References**:**Help with fitting***From:*ismail <ism45@yahoo.com>