SegRegA :   Fitting of logistic S-curves or sigmoids with confidence belt to cause-effect data.
Totally free download of software

Summary:
The amplified SegReg computer program (model), SegRegA, originally designed to perform a
segmented (piecewise) linear regression, has been given the possibility to fit quadratic parabola's,
cubic functions, and sigmoid S-curves to agricultural crop data, (see list of publications in which SegReg is used).
The cubic functions are determined by matrices, determinants and matrix inversion.
The third degree polygon can be used as a method to calculate and determine the salt tolerance of crops,
see this article published in the International Journal of Agricultural Science and entitled "Crop tolerance to soil salinity,
statistical analysis of data measured in farm lands".

Screenprint:

screenprint
         SegReg for S-curve preference

Download:
SegReg
standard

Download:
SegRegA
amplified

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Example of an S-curve model for crop yield and depth of the water table:

yield of barley
         and soil salinity


Example of an inverted S-curve model for crop yield and soil salinity :

yield of barley
         and soil salinity


Example of a cubic regression applied to crop yield and soil salinity yielding an S-curve :

a cubic 
         regression based in inverted matrix