RQGFIT

Name

rqgfit

Purpose

Fit a radial gaussian function to the input data (no linear term).

Description

Fit the equation y=f(r) where:
F(r) = A0*EXP(-z^2/2) + A2 + A3*r^2
and
z=r/A2
A0 = height of exp, A1 = sigma (the width).
A2 = constant term, A3 = quadratic term.
The parameters A0, A1, A2 are estimated and then CURVEFIT is
called. The gaussian is assumed to be centered at r=0.

Calling Sequence

Result = RQGAUSSFIT(R, Y [, A])

Inputs

R: The independent variable. R must be a vector.
Y: The dependent variable. Y must have the same number of points
as R.

Outputs

The fitted function is returned.

Optional Output Parameters

A: The coefficients of the fit. A is a four-element vector as
described under PURPOSE.

Common Blocks

None.

Side Effects

None.

Restrictions

Procedure

The initial guess of the intensity is the value of the point
with the smallest r value. The first point that drops below
half of the first is the guess at the width.

Modification History

DMS, RSI, Dec, 1983.
Rewritten to change initial guess, MWB, Lowell Obs., Dec. 1992.
Rewritten to remove linear term, MWB, Lowell Obs., Jan. 1993.