G = hartley (w, gain, phase, n, ordmax, type) This function returns a model for a plant with a known frequency behaviour. The model is either G(1)*s^(n*Q) + G(2)*s^((n-1)Q) + ... + G(end-2)*s^(2*Q) + G(end-1)*s^Q + G(end) or else the inverse of the above. The function receives the gain in dB and the phase in degrees for frequencies, in rad/s, specified in w. Parameter Q must be supplid; if n (the desired number of zeros and poles of the model) is not supplied, length(w)-1 is assumed instead; type may be 'num' or 'den' for the two types of models stated above: it may be ommited, the default being 'den'. Duarte Valério 2003