Function RTSEC(X1, X2, XACC)
    MAXIT = 30
    FL = FUNC(X1)
    F = FUNC(X2)
    If Abs(FL) < Abs(F) Then
        RTSEC = X1
        XL = X2
        SWAP = FL
        FL = F
        F = SWAP
    Else
        XL = X1
        RTSEC = X2
    End If
    For J = 1 To MAXIT
        DX = (XL - RTSEC) * F / (F - FL)
        XL = RTSEC
        FL = F
        RTSEC = RTSEC + DX
        F = FUNC(RTSEC)
        If Abs(DX) < XACC Or F = 0 Then Exit Function
    Next J
    Print "RTSEC exceed maximum iterations"
End Function