Re: Re: Fit function vs Hand Calculation

*To*: mathgroup at smc.vnet.net*Subject*: [mg104586] Re: [mg104528] Re: Fit function vs Hand Calculation*From*: DrMajorBob <btreat1 at austin.rr.com>*Date*: Wed, 4 Nov 2009 01:37:44 -0500 (EST)*References*: <4AEDB3D2.4010604@accardi.com> <4AEE0305.8070404@gmail.com>*Reply-to*: drmajorbob at yahoo.com

The jpeg is a time-waster; you could have put a notebook at the link, instead. BUT: all we need is code, and you don't need a notebook, a link, OR a picture for that. Here's a look at the problem: data = {{7, 1}, {5, 0}, {4, -1}}; g[x_] = InterpolatingPolynomial[data, x]; FindFit[data, a + b Log@x, {a, b}, x] f[x_] = a + b Log@x /. % {a -> -5.80756, b -> 3.52568} -5.80756 + 3.52568 Log[x] Show[Plot[{f@x, g@x}, {x, 0, 10}], Graphics[{PointSize[.02], Point@data}]] Show[Plot[f@x, {x, 3.9, 7.1}, PlotStyle -> Red], Graphics[{Blue, PointSize[.02], Point /@ data}], Plot[g@x, {x, 3.9, 7.1}, PlotStyle -> Blue]] InterpolatingPolynomial gives an exact fit, but the Fit function only tries to get close. In this case, I assume there's no function of the form a + b Log[x] that precisely fits your three points. Bobby On Tue, 03 Nov 2009 01:53:58 -0600, John Accardi <accardi at accardi.com> wrote: > Hello, > > Reading this forum I know my question is quite elementary. I am > new to Mathematica and have been pulling my hair out here (and I'm > bald to being with!). > > Any insights on this one? > > I assume a *.nb file can be attached here to this posting. It > contains the question. If not, it can be viewed here: > > http://www.accardi.com/zane.jpg > Thanks in advance for helping out. > > -- DrMajorBob at yahoo.com