Re: Surface fitting error while using Fit

*To*: mathgroup at smc.vnet.net*Subject*: [mg96561] Re: Surface fitting error while using Fit*From*: dh <dh at metrohm.com>*Date*: Mon, 16 Feb 2009 06:59:10 -0500 (EST)*References*: <gn8jb8$7oa$1@smc.vnet.net>

Hi Srikanth, you should give an full example. Otherwise I can not tell what you are doing wrong. Here is a working example: d = Flatten[Table[{x, y, x + 2 y + 3 x y + Random[]}, {x, 1.1, 1.9, 0.1}, {y,7.5, 10.5, 0.5}], 1]; Fit[d, {1, x, y, x y}, {x, y}] hope this helps, Daniel Srikanth wrote: > Hi > > I am using mathematica to fit data to a surface. My data is in a > matrix form: > Data1={{1.1, 7, 8.765}, {1.1, 7.5, 10.6481},.....,{1.9, 10.5, > 26.1048}} > > I want to get a form z=f(x,y) that fits this data, with x and y being > my first and second element of each vector. I expect the solution to > be a linear combination of x, y, xy and some constant term. > > So I tried > Fit[Data1, {1, x, y, xy}, {x, y}] > > and I get an error message: > Fit::fitm: Unable to solve for the fit parameters; the design matrix > is nonrectangular, non-numerical, or could not be inverted. > > I'm not sure what it meant by non-numerical (for example Data1[[1,1]] > gives 1.1 as expected). The data is rectangular and well defined (by > which I mean I never have cases like {x, , z} with y missing or > anything absurd like that). It cannot be inverted of course, but that > didn't seem to be a problem from the example 9 given here: > http://reference.wolfram.com/mathematica/tutorial/CurveFitting.html > > Any suggestions on what I need to do? > Thanks for your help > Srikanth >