/usr/share/octave/packages/control-2.6.2/sumblk.m is in octave-control 2.6.2-1build1.
This file is owned by root:root, with mode 0o644.
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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{S} =} sumblk (@var{formula})
## @deftypefnx{Function File} {@var{S} =} sumblk (@var{formula}, @var{n})
## Create summing junction @var{S} from string @var{formula}
## for name-based interconnections.
##
## @strong{Inputs}
## @table @var
## @item formula
## String containing the formula of the summing junction,
## e.g. @code{e = r - y + d}
## @item n
## Signal size. Default value is 1.
## @end table
##
## @strong{Outputs}
## @table @var
## @item S
## State-space model of the summing junction.
## @end table
##
## @strong{Example}
## @example
## @group
## octave:1> S = sumblk ('e = r - y + d')
##
## S.d =
## r y d
## e 1 -1 1
##
## Static gain.
## octave:2> S = sumblk ('e = r - y + d', 2)
##
## S.d =
## r1 r2 y1 y2 d1 d2
## e1 1 0 -1 0 1 0
## e2 0 1 0 -1 0 1
##
## Static gain.
## @end group
## @end example
## @seealso{connect}
## @end deftypefn
## Author: Lukas Reichlin <lukas.reichlin@gmail.com>
## Created: October 2013
## Version: 0.1
function s = sumblk (formula, n = 1)
if (nargin == 0 || nargin > 2)
print_usage ();
endif
if (! ischar (formula))
error ("sumblk: require string as first argument");
endif
if (! is_real_scalar (n))
error ("sumblk: require integer as second argument");
endif
if (length (strfind (formula, "=")) != 1)
error ("sumblk: formula requires exactly one '='");
endif
## if the first signal has no sign, add a plus
if (isempty (regexp (formula, "=\\s*[+-]", "once")))
formula = regexprep (formula, "=", "=+", "once");
endif
## extract operators, remove "=" from formula
operator = regexp (formula, "[=+-]", "match");
if (! strcmp (operator{1}, "="))
error ("sumblk: formula has misplaced '='");
endif
operator = operator(2:end);
formula = formula(formula != "=");
## extract signal names
signal = regexp (formula, "\\s*[+-]\\s*", "split");
if (any (cellfun (@isempty, signal)))
error ("sumblk: formula is missing some input/output names");
endif
outname = signal(1);
inname = signal(2:end);
signs = ones (1, numel (inname));
signs(strcmp (operator, "-")) = -1;
if (n != 1)
outname = strseq (outname{1}, 1:n);
tmp = cellfun (@strseq, inname, {1:n}, "uniformoutput", false);
inname = vertcat (tmp{:});
endif
d = kron (signs, eye (n));
s = ss (d);
s = set (s, "inname", inname, "outname", outname);
## NOTE: the dark side returns a tf, but i prefer an ss model
## because in general, transfer functions and mimo
## interconnections don't mix well
endfunction
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