Polynomial regression
Only PointLineSeries has properties/feature to do regression fitting for data points. Regression fitting, utilizing RegressionFitting and RegressionPolyOrder properties of PointLineSeries. When RegressionFitting is set other than None option, line replaced with fitted curve (see image below).
For other series it is possible to use MathRoutines.PolynomialRegression() method and replace data with fitted points.

An example of 3rd-order (cubic) polynomial regression fit.
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To see feature demonstration as example, check LineSeriesXYFeatures, ExampleRegression, SplineLineMouseEdit from our Demo.