References
- G. Martelli, Response to a setpoint change in PID controlled time-delay feedback systems, http://arxiv.org/abs/math.OC/0702663v1 22 February 2007
- Martelli , G. 2008 . A note on four-point partial difference equations with variable coefficients . J. Differ. Equ. Appl. , 14 ( 2 ) : 209 – 213 .