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## Copyright (C) 2009-2014 Lukas F. Reichlin
##
## This file is part of LTI Syncope.
##
## LTI Syncope is free software: you can redistribute it and/or modify
## it under the terms of the GNU General Public License as published by
## the Free Software Foundation, either version 3 of the License, or
## (at your option) any later version.
##
## LTI Syncope is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
## GNU General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with LTI Syncope. If not, see <http://www.gnu.org/licenses/>.
## -*- texinfo -*-
## @deftypefn {Function File} {@var{bool} =} isminimumphase (@var{sys})
## @deftypefnx {Function File} {@var{bool} =} isminimumphase (@var{sys}, @var{tol})
## Determine whether @acronym{LTI} system is minimum-phase.
## The zeros must lie in the left complex half-plane.
## The name minimum-phase refers to the fact that such a system has the
## minimum possible phase lag for the given magnitude response |sys(jw)|.
##
## @strong{Inputs}
## @table @var
## @item sys
## @acronym{LTI} system.
## @item tol
## Optional tolerance.
## @var{tol} must be a real-valued, non-negative scalar.
## Default value is 0.
## @end table
##
## @strong{Outputs}
## @table @var
## @item bool
## True if the system is minimum-phase and false otherwise.
## @end table
##
## @example
## @group
## real (z) < -tol*(1 + abs (z)) continuous-time
## abs (z) < 1 - tol discrete-time
## @end group
## @end example
## @end deftypefn
## Author: Lukas Reichlin <lukas.reichlin@gmail.com>
## Created: January 2011
## Version: 0.1
function bool = isminimumphase (sys, tol = 0)
if (nargin > 2)
print_usage ();
endif
z = zero (sys);
ct = isct (sys);
bool = __is_stable__ (z, ct, tol);
endfunction