##
POLYFITW

The
POLYFITW function performs a weighted
least-square polynomial
fit with optional error estimates and returns a vector of coefficients with a length of *
NDegree*
+1.

The POLYFITW routine uses matrix inversion. A newer version of this routine, SVDFIT, uses Singular Value Decomposition. The SVD technique is more flexible, but slower. Another version of this routine, POLY_FIT, performs a least square fit without weighting.

This routine is written in the IDL language. Its source code can be found in the file ```
polyfitw.pro
```

in the ```
lib
```

subdirectory of the IDL distribution.

###
Calling Sequence

Result = POLYFITW(*
X, Y, Weights, NDegree [,Yfit, Yband, Sigma, Corrm]*
)

###
Arguments

####
X

An *
n*
-element vector of independent variables.

####
Y

A vector of independent variables, the same length as *
X*
.

####
Weights

A vector of weights, the same length as *
X*
and *
Y*
.

####
NDegree

The degree of the polynomial to fit.

####
Yfit

A named variable that will contain the vector of calculated *
Y*
values. These values have an error of plus or minus *
Yband*
.

####
Yband

A named variable that will contain the error estimate for each point.

####
Sigma

A named variable that will contain the standard deviation of the returned coefficients.

####
Corrm

A named variable that will contain the correlation matrix of the coefficients.