User`s guide

3 Fitting Data
3-26
Default Coefficient Parameters
The default coefficient starting points and constraints for library and custom
models are given below. If the starting points are optimized, then they are
calculated heuristically based on the current data set. Random starting points
are defined on the interval [0,1] and linear models do not require starting
points.
If a model does not have constraints, the coefficients have neither a lower
bound nor an upper bound. You can override the default starting points and
constraints by providing your own values using the Fit Options GUI.
Note that the sum of sines and Fourier series models are particularly sensitive
to starting points, and the optimized values might be accurate for only a few
terms in the associated equations. For an example that overrides the default
starting values for the sum of sines model, refer to “Example: Sectioning
Periodic Data” on page 2-35.
Table 3-1: Default Starting Points and Constraints
Model Starting Points Constraints
Custom linear N/A None
Custom nonlinear Random None
Exponentials Optimized None
Fourier series Optimized None
Gaussians Optimized c
i
> 0
Polynomials N/A None
Power series Optimized None
Rationals Random None
Sum of sines Optimized b
i
> 0
Weibull Random a, b > 0