fitter.fitpoly - Function

Solve polynomial equations

Synopsis
fitpoly(n, x, y, sd, wt, id)

Arguments

n	in	the order of the polynomial to solve for
		Allowed:	integer
x	in	the parameter for the polynomial calculations
		Allowed:	one or more real or complex values
y	in	observed values of the condition equations
		Allowed:	N `x` m values
sd	in	standard deviation of equations
		Allowed:	one or more values used cyclically
		Default:	unset
wt	in	an optional alternate for sd
		Allowed:	one or more values used cyclically
		Default:	1
id	in	the id of a sub-tool
		Allowed:	fitter id
		Default:	0

Returns
bool

Description
fitpoly will create normal equations from the specified condition equations, and solve the resulting normal equations. In essence a combination of makepoly and fit.

The method expects that the properties of the fitter to be used have been initialized or set (like the number of simultaneous solutions m; the type; factors). The main reason is to limit the number of parameters on the one hand, and on the other hand not to depend on the actual array structure in Glish to get the variables and type.

Example

- include 'fitting.g'
- fit := fitter();		# a fitter for real unknowns
- x:=[1:10]			# we have values at 10 'x' values
- y:=2+0.5*x-0.1*x^2		# which are 2 +0.5x -0.1x^2
- fit.fitpoly(3,x,y) 		# fit a 3-degree polynomial
T 
- print fit.solution(), fit.error() #  show solution and their errors
[2 0.5 -0.1 -6.21725e-14]  [0 0 0 0]

Note the big problem with polynomial fitting if you have relatively large x values: the internal precision of computers start to play a role. In general it is worth the effort to normalize x between -1 and 1. To aid in most standard cases, a function fitspoly has been provided.

Next: fitter.fitspoly - Function Up: fitter - Tool Previous: fitter.fitavg - Function Contents Index

	Package	utility
	Module	fitting
	Tool	fitter