y[n] = 1/a0*(B x X –A x Y)
where y[n] is the output response
      B is a k-dimension vector – contains forward coefficients;
      X is a k-dimension vector – containing past k samples from the input signal;
      A is a (n-1)-dimension vector – reverse coeff.
      Y is a (n-1)-dimension vector – contains past n-1 outputs from the filter.