SAMPLED-DATA SIMULATION OF PERIODICALLY SWITCHED LINEAR CIRCUITS - Computer Methods for Analysis of Mixed-Mode Switching Circuits - page 130

and are changed to and
respectively. Because and can be
approximated from their Taylor series expansions of a finite terms
and
The algorithms for computing the time derivatives of and
are given in Appendix 6.C of this chapter. For small clock jitter, only
the first-order derivatives are usually needed. Note that for fixed T , the