EXTERNAL

SUB mnewt (ntrial, x(), n, tolx, tolf)

    ! Subroutine usrfun supplied by the user

    LIBRARY "ludcmp", "lubksb"

    DIM alpha(0,0), beta(0), indx(0)
    MAT redim alpha(n, n), beta(n), indx(n)

    FOR k = 1 to ntrial

        CALL usrfun (x(), alpha(,), beta())

        LET errf = 0
        FOR i = 1 to n
            LET errf = errf + abs(beta(i))
        NEXT i
        IF errf <= tolf then EXIT SUB

        CALL ludcmp (alpha(,), n, n, indx(), d)
        CALL lubksb (alpha(,), n, n, indx(), beta())

        LET errx = 0
        FOR i = 1 to n
            LET errx = errx + abs(beta(i))
            LET x(i) = x(i) + beta(i)
        NEXT i

        IF errx <= tolx then EXIT SUB

    NEXT k

END SUB