Order matters

Order among the x-coordinates of the breakpoints of a piecewise linear constraint matters.

If your XML model includes piecewise linear constraints (PWL), you must specify breakpoints in a PWL constraint in increasing order of the x-coordinates of the breakpoints. Otherwise, CPLEX cannot extract them as you intend.

As a demonstration of the effect of order among breakpoints, consider, for example, these breakpoints:

 
(0,0) (1,0) (1,1) (2,1)
(0,0) (1,1) (1,0) (2,1)

Both sets cite the same four breakpoints, but notice that the order is different. The first set specifies these two horizontal line segments:

 
                          _
(0,0) (1,0) (1,1) (2,1)  _

The second set specifies these two parallel line segments sloping at 45 degrees:

 
(0,0) (1,1) (1,0) (2,1) //