/usr/share/octave/packages/control-2.6.2/@frd/frd.m is in octave-control 2.6.2-1build1.
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##
## 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{sys} =} frd (@var{sys})
## @deftypefnx {Function File} {@var{sys} =} frd (@var{sys}, @var{w})
## @deftypefnx {Function File} {@var{sys} =} frd (@var{H}, @var{w}, @dots{})
## @deftypefnx {Function File} {@var{sys} =} frd (@var{H}, @var{w}, @var{tsam}, @dots{})
## Create or convert to frequency response data.
##
## @strong{Inputs}
## @table @var
## @item sys
## @acronym{LTI} model to be converted to frequency response data.
## If second argument @var{w} is omitted, the interesting
## frequency range is calculated by the zeros and poles of @var{sys}.
## @item H
## Frequency response array (p-by-m-by-lw). H(i,j,k) contains the
## response from input j to output i at frequency k. In the SISO case,
## a vector (lw-by-1) or (1-by-lw) is accepted as well.
## @item w
## Frequency vector (lw-by-1) in radian per second [rad/s].
## Frequencies must be in ascending order.
## @item tsam
## Sampling time in seconds. If @var{tsam} is not specified,
## a continuous-time model is assumed.
## @item @dots{}
## Optional pairs of properties and values.
## Type @command{set (frd)} for more information.
## @end table
##
## @strong{Outputs}
## @table @var
## @item sys
## Frequency response data object.
## @end table
##
## @strong{Option Keys and Values}
## @table @var
## @item 'H'
## Frequency response array. See 'Inputs' for details.
##
## @item 'w'
## Frequency vector. See 'Inputs' for details.
##
## @item 'tsam'
## Sampling time. See 'Inputs' for details.
##
## @item 'inname'
## The name of the input channels in @var{sys}.
## Cell vector of length m containing strings.
## Default names are @code{@{'u1', 'u2', ...@}}
##
## @item 'outname'
## The name of the output channels in @var{sys}.
## Cell vector of length p containing strings.
## Default names are @code{@{'y1', 'y2', ...@}}
##
## @item 'ingroup'
## Struct with input group names as field names and
## vectors of input indices as field values.
## Default is an empty struct.
##
## @item 'outgroup'
## Struct with output group names as field names and
## vectors of output indices as field values.
## Default is an empty struct.
##
## @item 'name'
## String containing the name of the model.
##
## @item 'notes'
## String or cell of string containing comments.
##
## @item 'userdata'
## Any data type.
## @end table
##
## @seealso{dss, ss, tf}
## @end deftypefn
## Author: Lukas Reichlin <lukas.reichlin@gmail.com>
## Created: February 2010
## Version: 0.1
function sys = frd (H = [], w = [], varargin)
## NOTE: * There's no such thing as a static gain
## because FRD objects are measurements,
## not models.
## * If something like sys1 = frd (5) existed,
## it would cause troubles in cases like
## sys2 = ss (...), sys = sys1 * sys2
## because sys2 needs to be converted to FRD,
## but sys1 contains no valid frequencies.
## * However, things like frd (ss (5)) should
## be possible.
## model precedence: frd > ss > zpk > tf > double
superiorto ("ss", "zpk", "tf", "double");
argc = 0; # initialize argument count
switch (nargin)
case 0 # empty object sys = frd ()
tsam = -2; # undefined sampling time
case 1
if (isa (H, "frd")) # already in frd form sys = frd (frdsys)
sys = H;
return; # nothing more to do here
elseif (isa (H, "lti")) # another lti object sys = frd (sys)
[sys, alti] = __sys2frd__ (H);
sys.lti = alti; # preserve lti properties
return; # nothing more to do here
else # sys = frd (H) *must* fail
print_usage ();
endif
case 2
if (isa (H, "lti")) # another lti object sys = frd (sys, w)
[sys, alti] = __sys2frd__ (H, w);
sys.lti = alti; # preserve lti properties
return; # nothing more to do here
else # sys = frd (H, w)
tsam = 0; # continuous-time
endif
otherwise # default case
argc = numel (varargin); # number of additional arguments after H and w
if (issample (varargin{1}, -10)) # sys = frd (H, w, tsam, "prop1", val1, ...)
tsam = varargin{1}; # sampling time, could be 0 as well
argc--; # tsam is not a property-value pair
if (argc > 0) # if there are any properties and values ...
varargin = varargin(2:end); # remove tsam from property-value list
endif
else # sys = frd (H, w, "prop1", val1, ...)
tsam = 0; # continuous-time
endif
endswitch
[H, w] = __adjust_frd_data__ (H, w);
[p, m] = __frd_dim__ (H, w); # determine number of outputs and inputs
frdata = struct ("H", H, "w", w); # struct for frd-specific data
ltisys = lti (p, m, tsam); # parent class for general lti data
sys = class (frdata, "frd", ltisys); # create frd object
if (argc > 0) # if there are any properties and values, ...
sys = set (sys, varargin{:}); # use the general set function
endif
endfunction
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