function engine = filter_engine(tbn_engine)% FILTER_ENGINE Create an engine which does online filtering% function engine = filter_engine(tbn_engine)engine.tbn_engine = tbn_engine;engine.f = [];  % space to store filtered messageengine.old_f = [];engine.b = []; % space to store smoothed messageengine.t = [];engine = class(engine, 'filter_engine');