%% Copyright (C) 2014, 2016, 2018-2019, 2022 Colin B. Macdonald
%%
%% This file is part of OctSymPy.
%%
%% OctSymPy 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 software 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 software; see the file COPYING.
%% If not, see <http://www.gnu.org/licenses/>.

%% -*- texinfo -*-
%% @documentencoding UTF-8
%% @defop  Method   @@symfun minus {(@var{f}, @var{g})}
%% @defopx Operator @@symfun {@var{f} - @var{g}} {}
%% Subtract one symbolic function from another.
%%
%% Example:
%% @example
%% @group
%% syms x
%% f(x) = 2*x;
%% g(x) = sin(x);
%% @end group
%%
%% @group
%% h = f - g
%%   @result{} h(x) = (symfun) 2⋅x - sin(x)
%% @end group
%% @end example
%%
%% Matrix example:
%% @example
%% @group
%% syms x y
%% f(x, y) = sym([1 12; 13 4]);
%% g(x, y) = [x 0; 0 y];
%% @end group
%%
%% @group
%% h = g - f
%%   @result{} h(x, y) = (symfun)
%%       ⎡x - 1    -12 ⎤
%%       ⎢             ⎥
%%       ⎣ -13    y - 4⎦
%% @end group
%% @end example
%%
%% @seealso{@@symfun/plus, @@symfun/uminus}
%% @end defop

function h = minus(f, g)
  [vars, s1, s2] = helper_symfun_binops(f, g);
  h = symfun(s1 - s2, vars);
end


%!test
%! syms x
%! f(x) = x^2;
%! assert( isa(f - f, 'symfun'))
%! assert( isa(f - x, 'symfun'))

%!test
%! % Octave bug #42735 fixed in 4.4.2
%! syms x
%! f(x) = x^2;
%! g = x^2;
%! h = x - f;  assert (isa (h, 'symfun') && isequal (formula (h), x - g))
%! h = x + f;  assert (isa (h, 'symfun') && isequal (formula (h), x + g))
%! h = x * f;  assert (isa (h, 'symfun') && isequal (formula (h), x * g))
%! h = x / f;  assert (isa (h, 'symfun') && isequal (formula (h), x / g))
%! h = x ^ f;  assert (isa (h, 'symfun') && isequal (formula (h), x ^ g))
%! h = x .* f; assert (isa (h, 'symfun') && isequal (formula (h), x .* g))
%! h = x ./ f; assert (isa (h, 'symfun') && isequal (formula (h), x ./ g))
%! h = x .^ f; assert (isa (h, 'symfun') && isequal (formula (h), x .^ g))

%!test
%! % different variables
%! syms x y
%! f(x) = 2*x;
%! g(y) = sin(y);
%! h = f - g(x);
%! assert( isa(h, 'symfun'))
%! assert( isequal (argnames (h), argnames (f)))
%! assert (isequal (formula (h), 2*x - sin(x)))
%! % and even if rh-sym has a dummy variable:
%! h = f - g(y);
%! assert( isa(h, 'symfun'))
%! assert( isequal (argnames (h), argnames(f)))
%! assert (isequal (formula (h), 2*x - sin(y)))

%!test
%! % different variables, f has more
%! syms x y
%! f(x,y) = 2*x*y;
%! g(y) = sin(y);
%! h = f - g(y) + g(x);
%! assert( isa(h, 'symfun'))
%! assert( isequal (argnames (h), argnames (f)))
%! assert (isequal (formula (h), 2*x*y - sin(y) + sin(x)))
