Editing Piecewise linear function (section)

== Applications ==

[[File: R-3VAR1.JPG|thumb|left|Crop response to depth of the watertable<ref>[https://www.waterlog.info/segreg.htm A calculator for piecewise regression].</ref>]]
[[File:Mustard segm regr no effect.png|thumb|right|Example of crop response to soil salinity<ref>[https://www.waterlog.info/partreg.htm A calculator for partial regression].</ref>]]

In [[agriculture]] piecewise [[regression analysis]] of measured data is used to detect the range over which growth factors affect the yield and the range over which the crop is not sensitive to changes in these factors.

The image on the left shows that at shallow [[watertable]]s the yield declines, whereas at deeper (> 7 dm) watertables the yield is unaffected. The graph is made using the method of [[least squares]] to find the two segments with the [[best fit]].

The graph on the right reveals that crop yields [[salt tolerance of crops|tolerate]] a [[soil salinity]] up to ECe = 8 dS/m (ECe is the electric conductivity of an extract of a saturated soil sample), while beyond that value the crop production reduces. The graph is made with the method of partial regression to find the longest range of "no effect", i.e. where the line is horizontal. The two segments need not join at the same point. Only for the second segment method of least squares is used.
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