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    function f = thisisstable(Hd)
%THISISSTABLE  True if filter is stable.
%   THISISSTABLE(Hd) returns 1 if discrete-time filter Hd is stable, and 0
%   otherwise. 

%   Author(s): R. Losada, T. Bryan
%   Copyright 1988-2002 The MathWorks, Inc.

% This should be private

f = thisisstable(Hd.privAllpass1) & thisisstable(Hd.privAllpass2);