Piecewise Function With Two Segments

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Piecewise Function With Two Segments

Fit a function consisting of two linear segments that bend at X=5. When X is less than 5, the slope of the function is B1. When X is greater than or equal to 5, the slope is B2. B0 is the Y value of the function at X=5 (i.e., at the pivot point). The if statement is used to control which function model is used depending on whether the value of the dependent variable is greater than or less than the pivot point.

Title "Piecewise linear function";
Variables X,Y;
Parameter B0;
Parameter B1;
Parameter B2;
Constant Pivot=5;		// X value at which bend occurs
if (x < Pivot) {
    Function Y = B0+B1*(X-Pivot);
} else {
    Function Y = B0+B2*(X-Pivot);
}
Plot residual;
Rplot grid;
Data;
[ data goes here ]