
   integrate (x) (y) (start) (end)

   Perform an integration of (y) as a function of (x) from (start) to (end)

   The result is placed into the variable: $sum

   Caution!: Program uses the front end of each x bin to approximate the integral.
    Very coarse bins (delta x = 1) over small regions (x=1->5) can introduce
    errors as large as 20%. Fine bins are reccommended.
