Finds the slope at x in the lookup lookup according to the mode m. Between points on a Lookup the slope is just the change in y divided by the change in x from one point to the next. If x is the same as a point in lookup then the average of the slope before and after x is returned, unless there is more than one point with that x value in which case :NA: is returned.
If the value for x is outside the domain of lookup (bigger than the biggest x point or smaller than the smallest x point) what is returned depends on m, If m is 0 then 0 is returned, this is analogous to a normal lookup. If m is 1 then the slope of the closes segment is used (this is analogous to LOOKUP EXTRAPOLATE). If m is -1 then :NA: is returned.
Units: LOOKUP SLOPE(units,dmnl,dmnl) --> units
Example
LOOK((0,1),(1,1),(2,3))
LOOKUP SLOPE(LOOK,-1,-1) is equal to :NA:
LOOKUP SLOPE(LOOK,-1,0) is equal to 0
LOOKUP SLOPE(LOOK,-1,1) is equal to 1
LOOKUP SLOPE(LOOK,1,0) is equal to .75
LOOKUP SLOPE(LOOK,0.5,0) is equal to 1
LOOKUP SLOPE(LOOK,1.5,0) is equal to .5
Availability: Not PLE or PLE Plus
See also: LOOKUP AREA, VECTOR LOOKUP, Lookups
Sample model: LOOKUP functions.mdl in FunctionExamples
