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## Copyright 2015 Oliver Heimlich
## Copyright 2017 Joel Dahne
##
## This program 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.
##
## This program 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 this program; if not, see <http://www.gnu.org/licenses/>.
## -*- texinfo -*-
## @documentencoding UTF-8
## @defun ctc_intersect (@var{C1}, @var{Y1}, @var{C2}, @var{Y2})
## @defunx ctc_intersect (@var{C1}, @var{C2})
##
## Return a contractor function for the intersection of two sets.
##
## Functions @var{C1} and @var{C2} define two sets @code{S1 = @{@var{x} |
## @var{C1} (@var{x}) ∈ @var{Y1}@}} and @code{S2 = @{@var{x} |
## @var{C2} (@var{x}) ∈ @var{Y2}@}}. The return value is a contractor function
## for the set @code{S1 ∩ S2 = @{@var{x} | @var{C1} (@var{x}) ∈ @var{Y1} and
## @var{C2} (@var{x}) ∈ @var{Y2}@}}.
##
## Parameters @var{C1} and @var{C2} must be function handles and must accept
## the same number of parameters. See @command{@@infsup/fsolve} for how to
## define contractor functions. The user manual also contains an example on
## how to use this function.
##
## Instead of solving @code{@var{C1} (@var{x}) ∈ @var{Y1}} and
## @code{@var{C2} (@var{x}) ∈ @var{Y2}} separately and then compute an
## intersection of the result, you can solve
## @code{ctc_intersect (@var{C1}, @var{Y1}, @var{C2}, @var{Y2}) = 0}.
##
## @seealso{@@infsup/fsolve, ctc_union}
## @end defun
## Author: Oliver Heimlich
## Keywords: interval
## Created: 2015-12-20
function c = ctc_intersect (ctc1, y1, ctc2, y2)
## Reorder parameters
switch (nargin)
case 2
ctc2 = y1;
y1 = y2 = 0;
case 3
if (is_function_handle (y1))
y2 = ctc2;
ctc2 = y1;
y1 = 0;
else
y2 = 0;
endif
case 4
...
otherwise
print_usage ();
endswitch
## Check parameters
if (not (isa (y1, "infsup")))
y1 = infsup (y1);
endif
if (not (isa (y2, "infsup")))
y2 = infsup (y2);
endif
if (not (is_function_handle (ctc1)) && not (ischar (ctc1)))
error ("interval:InvalidOperand", ...
"ctc_intersect: Parameter C1 is no function handle")
endif
if (not (is_function_handle (ctc2)) && not (ischar (ctc2)))
error ("interval:InvalidOperand", ...
"ctc_intersect: Parameter C2 is no function handle")
endif
c = @(varargin) ctc_intersect_eval (ctc1, y1, ctc2, y2, varargin{:});
endfunction
function varargout = ctc_intersect_eval (ctc1, y1, ctc2, y2, varargin)
y = varargin{1};
x = varargin(2 : end);
## Always return at least one value
if nargout == 0
nargout = 1;
endif
## Evaluate each contractor function
fval_and_contractions1 = nthargout (1 : nargout, ctc1, y1, x{:});
fval_and_contractions2 = nthargout (1 : nargout, ctc2, y2, x{:});
if nargout == 1
fval_and_contractions1 = {fval_and_contractions1};
fval_and_contractions2 = {fval_and_contractions2};
endif
## Compute fval = y if both function values are inside of their constraints
fval1 = fval_and_contractions1{1};
fval2 = fval_and_contractions2{1};
fval1 = y + y_dist (y1, fval1);
fval2 = y + y_dist (y2, fval2);
varargout{1} = union (fval1, fval2);
## Both contractors must produce a subset of y.
varargout{1}(disjoint (fval1, y) | disjoint (fval2, y)) = infsup ();
## Combine the contractions
for i = 2 : nargout
varargout{i} = intersect (fval_and_contractions1{i}, ...
fval_and_contractions2{i});
endfor
endfunction
function d = y_dist (y, fval)
d = infsup (idist (y, fval), hdist (y, fval));
d(subset (fval, y) & not (isempty (fval))) = 0;
for i = 1:ndims (y)
if (size (y, i) != 1)
d = sum (d, i);
endif
endfor
endfunction
%!function [fval, x] = ctc_abs (y, x)
%! fval = abs (x);
%! x = absrev (intersect (fval, y), x);
%!endfunction
%!shared c
%! c = ctc_intersect (@ctc_abs, "[0, 2]", @ctc_abs, "[1, 3]");
%!test
%! [fval, x] = c (infsup (0), infsup ("[1, 3]"));
%! assert (ismember (0, fval) && 0 != fval);
%! assert (x == infsup ("[1, 2]"));
%!test
%! [fval, x] = c (infsup (0), infsup ("[1, 2]"));
%! assert (0 == fval);
%! assert (x == infsup ("[1, 2]"));
%!test
%! [fval, x] = c (infsup (0), infsup ("[entire]"));
%! assert (ismember (0, fval) && 0 != fval);
%! assert (x == infsup ("[-2, 2]"));
%!test
%! [fval, x] = c (infsup (0), infsup ("[0, inf]"));
%! assert (ismember (0, fval) && 0 != fval);
%! assert (x == infsup ("[1, 2]"));
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