% sos.m - second order section%% [y, w] = sos(b, a, w, x)%% b = [b0, b1, b2] = 3-dim numerator% a = [1,  a1, a2] = 3-dim denominator% w = 3-dim filter state (row vector)% x = scalar input% y = scalar output% based on sos.cfunction [y, w] = sos(b, a, w, x)w(1) = x - a(2) * w(2) - a(3) * w(3);y = b(1) * w(1) + b(2) * w(2) + b(3) * w(3);w(3) = w(2);w(2) = w(1);