MODULE trapzd

    SHARE it, s                   ! STATIC, must be preserved between calls

    SUB trapzd (dum, a, b, s, n)

        DECLARE FUNCTION func     ! Supplied by the user

        IF n = 1 then
           LET s = .5 * (b - a) * (func(a) + func(b))
           LET it = 1
        ELSE
           LET tnm = it
           LET del = (b - a) / tnm
           LET x = a + .5 * del
           LET sum = 0
           FOR j = 1 to it
               LET sum = sum + func(x)
               LET x = x + del
           NEXT j
           LET s = .5 * (s + (b - a) * sum / tnm)
           LET it = 2 * it
        END IF

    END SUB

END MODULE