EXTERNAL

SUB zbrac (dum, x1, x2, succes)

    DECLARE FUNCTION func         ! Supplied by the user

    LET factor = 1.6
    LET ntry = 50
    IF x1 = x2 then
       PRINT "You have to guess an initial range"
       EXIT SUB
    END IF

    LET f1 = func(x1)
    LET f2 = func(x2)
    LET succes = -1
    FOR j = 1 to ntry
        IF f1 * f2 < 0 then EXIT SUB
        IF abs(f1) < abs(f2) then
           LET x1 = x1 + factor * (x1 - x2)
           LET f1 = func(x1)
        ELSE
           LET x2 = x2 + factor * (x2 - x1)
           LET f2 = func(x2)
        END IF
    NEXT j
    LET succes = 0

END SUB