clip function
The clip function of the form:
clip(out_a, out_b, in_a, in_b)
returns out_a if in_a > in_b, out_b otherwise. It’s usually implemented to produce a change at a certain date. For example, for equation:
val_1 = 1
val_2 = 2
pyear = 2002
val.k = clip(val_1, val_2, pyear, time.k)
the variable val will change from val_1 to val_2 at time pyear.