group delay Lp IIR filter optimization
[lt,grad]=iirgroup(p,r,theta,omega,wt,td)
Lp criterion
vector of the module of the poles and the zeros of the filters
vector of the argument of the poles and the zeros of the filters
frequencies where the filter specifications are given
weighting function for and the group delay
desired group delay
criterium and gradient values
optimization of IIR filters for the Lp criterium for the the group delay. (Rabiner & Gold pp270-273).