nonlinear filter?

[Francesco Potorti`]

I want to solve for Q in an expression like:
 Q(i) = Q(i-1) + I(i) - Q(i)
 U(i) = f(Q(i-1), I(i-1))

Given a vector I, I can find Q using filter() if f() is linear.  Is
there a way to solve this problem when f is not linear using Octave
other than looping through all elements of Q?

-- 
Francesco Potortì (ricercatore)        Voice: +39 050 315 3058 (op.2111)
ISTI - Area della ricerca CNR          Fax:   +39 050 315 2040
via G. Moruzzi 1, I-56124 Pisa         Email: address@hidden
Web: http://fly.isti.cnr.it/           Key:   fly.isti.cnr.it/public.key