Re: Making a function from the output of the Fit

*To*: mathgroup at smc.vnet.net*Subject*: [mg121554] Re: Making a function from the output of the Fit*From*: Daniel Lichtblau <danl at wolfram.com>*Date*: Mon, 19 Sep 2011 07:07:05 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com

----- Original Message ----- > From: "Just A Stranger" <forpeopleidontknow at gmail.com> > To: mathgroup at smc.vnet.net > Sent: Saturday, September 17, 2011 5:25:53 AM > Subject: Making a function from the output of the Fit function. > Hello, > > So I am trying to use the Fit ffunction to make another function. > > So I want to do something like this: > > f[x_] := Fit[ data, {1,x}, x] > > But I want f[x] to be the function for the line, a+bx. But as written > above > it does not have this result of course (I know it's because whatever > gets > passed is used as an argument for the fit function, so passing a > number > doesn't work, and passing a variable simply isn't what I want to do) > So how > can I use the fit function to get > f[x_] := a+bx (where a and b are the appropriate constants. ) > > My jerry rigged solution is to just execute Fit[ data, {1,x}, x] then > copy > and past the output to define a function. But this tacky solution just > won't > do :) > > Thank you for your help mathgroup. Might be easier to use FindFit. In[49]:= data = Table[{j, 3*j - 2}, {j, 20}] + RandomReal[{-.1, .1}, {20, 2}]; Now one can do In[58]:= a + b*x /. FindFit[data, a + b*x, {a, b}, x] Out[58]= -1.939582811115561 + 2.994503289542548 x or In[61]:= f[x_] = a + b*x /. FindFit[data, a + b*x, {a, b}, x] Out[61]= -1.939582811115561 + 2.994503289542548 x Many years ago I used the term "jerry rigged" in some in-house email. I was informed that it is not proper phraseology. It seems that "jury rig" and "jerry build" are quite different in meaning. Several years after that incident, I noticed "jerry rigged" in a James Ellroy novel (White Jazz, I think it was). It seems that the term has entered the language as a crossover of sorts. http://www.wordcourt.com/archives.php?show04-03-10 http://en.wikipedia.org/wiki/Jury_rig http://www.answerbag.com/q_view/9245 Daniel Lichtblau Wolfram Research