Christoph Läubrich created MATH-1534:
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Summary: GaussianCurveFitter.ParameterGuesser uses supicious
halfHeight calculations
Key: MATH-1534
URL: https://issues.apache.org/jira/browse/MATH-1534
Project: Commons Math
Issue Type: Bug
Affects Versions: 3.6.1, 4.0
Reporter: Christoph Läubrich
I'm currently looking into some curve-fitting and have examined the
basicGuess(WeightedObservedPoint[])
in GaussianCurveFitter.ParameterGuesser, and there is one thing I don't really
understand.
in [Line
301|https://github.com/apache/commons-math/blob/master/src/main/java/org/apache/commons/math4/fitting/GaussianCurveFitter.java#L301
] the "halfY" is computed by n (what is the maximal y value of the
observation) + half the sum of n+m (where m is the x value of the maximum)
applying this to some of my datapoints that fit relatively good as a Gaussian
later, it seems that this condition never works (assuming that max X != 0), and
the default in the catch clause is used instead. It seems that the optimizer is
quite well in fitting the data anyways.
[~erans] also suggested on the mailinglist that:
{quote}it seems that the current code could be made more robust by
shifting the abscissa of the maximum height to 0 before performing
the rest of the computation{quote}
For my own "guessing" I used the following strategy, I'm not sure if the
current code does something similar:
# Use p[0] and p[max] to form a line, then use PolynomialCurveFitter to fit
the line to all points on the left
# Use the fitted line to calculate Xleft at Ymax
# do the same for the rigtht portion
# Assume fwhm = rightX-leftX
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