Polyphase decomposition of IIR filter Is there a way to decompose IIR filter into set of poly phase components, that are All pass. E.g. a an IIR filter  of order M, can be decomposed into a cascade of All zero filter of order 2*M( which can be implemented as polyphase) and all pole of same order( as Direct form), by rationalizing the Denominator. But, I have not been able to find a way to do it directly as sum of all pass polyphase components.

any help?
Using matlabs tf2cl, it may require the DSP toolbox, you can turn the transsfer function (numerator and denominator coefficients) in to a cascade allpass lattice coefficients, which is a two phase filter.

% Generate some IIR filter coefficients
[b,a]=cheby1(9,.5,.4);

% Coupled allpass decomposition
[k1,k2]=tf2cl(b,a);