!  Fit a piecewise linear function that pivots at X=5.
!  When X is less than 5, the slope is B1.
!  When X is greater than or equal to 5, the slope is B2.
!  B0 is the Y value when X=5 (i.e., at the pivot point).
Title Piecewise linear function
Register
Variables X,Y
Parameters B0,B1,B2
Constant Pivot=5	! X value at which bend occurs
Function Y = step(X,Pivot)*(B0+B1*(X-Pivot)) + step(Pivot,X)*(B0+B2*(X-Pivot))
Plot g
Rplot g
Data
1.0000        9.0640
1.1429        9.3975
1.2857        9.2018
1.4286        9.2857
1.5714        8.9093
1.7143        9.3477
1.8571        9.0515
2.0000        8.8722
2.1429        9.3411
2.2857        8.8253
2.4286        8.9658
2.5714        8.4049
2.7143        8.4536
2.8571        8.8517
3.0000        8.8919
3.1429        8.4210
3.2857        8.7708
3.4286        8.6519
3.5714        8.4829
3.7143        8.0907
3.8571        7.9835
4.0000        8.0832
4.1429        8.2473
4.2857        7.5845
4.4286        7.6238
4.5714        7.6233
4.7143        7.5825
4.8571        7.7350
5.0000        7.6635
5.1429        7.6477
5.2857        7.1760
5.4286        7.2312
5.5714        7.1163
5.7143        6.8115
5.8571        6.8880
6.0000        6.7678
6.1429        6.4633
6.2857        6.0894
6.4286        5.7891
6.5714        6.1622
6.7143        5.9032
6.8571        5.8183
7.0000        5.4021
7.1429        5.2677
7.2857        5.3045
7.4286        5.1546
7.5714        4.7516
7.7143        4.8867
7.8571        4.5282
8.0000        4.6656