User`s guide

fittype
4-115
Create a fit type object for the rat33 library model. Note that the display
includes the full equation.
ftype = fittype('rat33')
ftype =
General model Rat33:
ftype(p1,p2,p3,p4,q1,q2,q3,x) = (p1*x^3 + p2*x^2 + p3*x + p4)/
(x^3 + q1*x^2 + q2*x + q3)
Create a fit type object and include the existing fit options object opts, and fit
to the census data.
load census
opts = fitoptions('Method','Nonlinear','Normalize','On');
ftype = fittype('a*exp(b*x)+c','options',opts);
f1 = fit(cdate,pop,ftype);