Name

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rgfit

Purpose

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Fit a radial gaussian function and 2nd order polynominal to the input data.

Description

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  Fit the equation y=f(r) where:
  F(r) = A0*EXP(-z^2/2) + A2 + A3*r + A4*r^2
  and
z=r/A2
A0 = height of exp, A1 = sigma (the width).
A2 = constant term, A3 = linear term, A4 = quadratic term.
  The parameters A0, A1, A2 are estimated and then CURVEFIT is
called. The gaussian is assumed to be centered at r=0.

Category

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Function fitting

Calling Sequence

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

Inputs

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

Outputs

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The fitted function is returned.

Optional Output Parameters

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

Common Blocks

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None.

Side Effects

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None.

Restrictions

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Procedure

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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.
If the (MAX-AVG) of Y is larger than (AVG-MIN) then it is assumed
that the line is an emission line, otherwise it is assumed there
is an absorbtion line. The estimated center is the MAX or MIN
element. The height is (MAX-AVG) or (AVG-MIN) respectively.
The width is found by searching out from the extrema until
a point is found less than the 1/e value.

Modification History

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DMS, RSI, Dec, 1983.
Rewritten to change initial guess, MWB, Lowell Obs., Dec. 1992.
93/05/11, put in failsafe on gaussian width guess, MWB, Lowell Obs.