Re: How to assign the result from NonlinearFit to a function

*To*: mathgroup at smc.vnet.net*Subject*: [mg70231] Re: How to assign the result from NonlinearFit to a function*From*: Bill Rowe <readnewsciv at sbcglobal.net>*Date*: Sun, 8 Oct 2006 02:04:49 -0400 (EDT)

On 10/7/06 at 7:09 AM, PengYu.UT at gmail.com wrote: >I have the following code. I want to assign the resulting function >of NonlinearFit to function f. But it seems that it doesn't work. >Would you please help me? ><< Statistics`NonlinearFit` >data = {{1.0, 1.0, .126}, {2.0, 1.0, .219}, {1.0, 2.0, .076}, {2.0, >2.0, .126}, {.1, .0, .186}}; >f[theta1_, theta2_, theta3_] := NonlinearFit[data, theta1 theta3 >x1/(1 + theta1 x1 + theta2 \ x2), {x1, x2}, {theta1, theta2, >theta3}] Part of the problem you are having is you are defining the function f to take as arguments the parameters you are asking NonlinearFit to find. That is f cannot depend on the arguments you supply as Nonlinear fit will replace them with numerical values determined by the data. Perhaps you want something like the following In[23]:= f[x_, y_] := Evaluate[NonlinearFit[data, theta1*theta3*(x1/(1 + theta1*x1 + theta2*x2)), {x1, x2}, {theta1, theta2, theta3}]] /. Thread[{x1, x2} -> {x, y}] In[24]:= f[x,y] Out[24]= (2.442770155675669*x)/(3.1315052420200065*x + 15.159362112360792*y + 1) In[25]:= f[1,2] Out[25]= 0.0709072 Note, the built in function FindFit does everything NonlinerFit does. So, this same result could be obtained as: In[27]:= g[x_, y_] := (theta1*theta3*x)/(theta1*x + theta2*y + 1) /. Evaluate[FindFit[data, (theta1*theta3*x1)/ (theta1*x1 + theta2*x2 + 1), {theta1, theta2, theta3}, {x1, x2}]] In[28]:= g[x,y] Out[28]= (2.442770155675669*x)/(3.1315052420200065*x + 15.159362112360792*y + 1) In[29]:= g[1,2] Out[29]= 0.0709072 -- To reply via email subtract one hundred and four