producing an equation to fit on a plotted data

hi all, according to this code and data is there anyway to get an polynomial with low degree( for example 2nd order)or a surface equation to fit our data??please help me what should i do to fit an equation on my data.

http://mathworks.com/matlabcentral/answers/10967-plotting-set-of-data-3d

 code:

data =[0,1,1;0,2,1.02;0,3,1.11;0,4,1.21;0,5,1.30;0,6,1.4;0,7,1.59;0,8,1.78; 10,1,1;10,2,1.11;10,3,1.35;10,4,1.62;10,5,1.95;10,6,2.33;10,7,3.34;10,8,4.77; 20,1,1.01;20,2,1.39;20,3,2.12;20,4,3.29;20,5,5.17;20,6,8.29;20,7,22;20,8,61; 30,1,1.13;30,2,2.5;30,3,6.36;30,4,17.5;30,5,50;30,6,150;30,7,1400;30,8,14800];

mn = arrayfun(@(i1)length(unique(data(:,i1))),2:-1:1); c = mat2cell(reshape(data,mn(1),mn(2),[]),mn(1),mn(2),[1 1 1]); surf(c{:})

Answer 1

[bym]

create a design matrix of your x & y values like this:

d = [ones(length(data),1),data(:,1),data(:,2),...
data(:,1).^2,data(:,1).*data(:,2),data(:,2).^2];

this represents [ constant, x, y, x^2, x*y, y^2]. Then, to find the coefficients do:

c = d\data(:,3)

[milad babaei]

thank u...

[milad babaei]

is there anyway to evaluate the values which are fitted by the equation???

[milad babaei]

i run the code >>3.6228426607 is this the constant of equation???this fitted equation be cause of large range of data doesnt fit well..would u plz help me finding another type of equations to fit well?

Answer 2

[Image Analyst]

Perhaps these File Exchange submissions:

http://www.mathworks.com/matlabcentral/fileexchange/31636-2d-polynomial-fitting-with-svd

http://www.mathworks.com/matlabcentral/fileexchange/13719-2d-weighted-polynomial-fitting-and-evaluation

Answer 3

[Rick Rosson]

Please try:

   sftool

or

   cftool

HTH.

[milad babaei]

would u please explain more on using sftool??