Thu Mar 7 21:54:11 EST 2013

Filter transforms

- Forward/backward diff
- Bilinear[1]
- Impulse invariance (exponential pole mapping) [2]
- Matched-Z (exponential pole/zero mapping) [3]

Forward/backward diff is simplest, but has stability issues for very
resonant poles.  Only works in the limit when poles/zeros go to s=0

Bilinear maps zeros at infinity to zeros at -1 while exponential
essentially samples the impulse response.

[1] http://en.wikipedia.org/wiki/Bilinear_transform
[2] http://en.wikipedia.org/wiki/Impulse_invariance
[3] http://en.wikipedia.org/wiki/Matched_Z-transform_method