EXTERNAL

FUNCTION rtnewt (dum, x1, x2, xacc)

    ! The subroutine funcd is supplied by the user

    LET jmax = 20
    LET trtnewt = .5 * (x1 + x2)
    FOR j = 1 to jmax

        CALL funcd (trtnewt, f, df)

        LET dx = f / df
        LET trtnewt = trtnewt - dx
        IF (x1 - trtnewt) * (trtnewt - x2) < 0 then
           PRINT "Jumped out of brackets"
           EXIT FUNCTION          ! Error exit
        END IF
        LET rtnewt = trtnewt
        IF abs(dx) < xacc then EXIT FUNCTION     ! Normal exit
    NEXT j
    PRINT "rtnewt exceeding maximum iterations"

END FUNCTION