Re: Fitting data to line with a specific slope
- To: mathgroup at smc.vnet.net
- Subject: [mg30629] Re: [mg30618] Fitting data to line with a specific slope
- From: BobHanlon at aol.com
- Date: Fri, 31 Aug 2001 19:58:05 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
In a message dated 2001/8/31 4:28:34 AM, cdneish at interchange.ubc.ca writes: >I am attempting to fit my data to a line of the form > > y = -3.2 x + intercept, > >but I cannot figure out how to do this with Mathematica. > >The function "Fit" takes only basis functions, so I cannot specify that >I >would like the slope to be -3.2. I also tried "NonlinearFit," but the >following code > > NonlinearFit[data, intercept - 3.2 x, x, intercept] > >yielded the following error message: > >Tranpose::nmtx : The first two levels of the one-dimensional list {} cannot >be transposed >Tranpose::nmtx : The first two levels of the one-dimensional list {-3.2} >cannot be transposed >NonlinearFit::lnnosvd : NonlinearFit was unable to obtain the singular >value >decomposition for the design matrix of the linear model. >NonlinearFit::fitfail : The fitting algorithm failed. > > >It is possible that my data does not fit a line with slope -3.2 very well. >Could this be the source of the errors? > >Any advice regarding these problems would be greatly appreciated. > I do not encounter the error message that you saw Needs["Graphics`Colors`"]; data = Table[{x, -3.2x+5+3(2Random[]-1)}, {x, 0, 10}]; intercept = Fit[data /. {x_, y_} :> {x, 3.2x+y}, {1}, x] 4.870101185989491 Plot[-3.2x+intercept, {x, 0, 10}, PlotStyle -> Blue, Epilog -> {Red, AbsolutePointSize[3], Point /@ data}]; Needs["Statistics`NonlinearFit`"]; Clear[intercept]; NonlinearFit[data, -3.2x+ intercept, x, intercept] 4.8701011859894905 - 3.2*x Bob Hanlon Chantilly, VA USA