@symfun/isequaln: implemented isequaln to support NaN's equality in @…

…symfun (fixes #740)

Added inst/@symfun/isequaln to check for NaN's equality.
FIX ME: Not a best way to tackle the problem. Might need further investigation in future.
See the discussion in #749

inst/@symfun/isequaln.m

@@ -0,0 +1,114 @@
+%% Copyright (C) 2017 NVS Abhilash
+%%
+%% 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
+%% @defmethod  @@symfun isequaln (@var{f}, @var{g})
+%% @defmethodx @@symfun isequaln (@var{f}, @var{g}, @dots{})
+%% Test if contents of two or more arrays are equal, even with nan.
+%%
+%% Example:
+%% @example
+%% @group
+%% syms x
+%% f(x) = x + 1;
+%% g(x) = x + 1;
+%% isequaln(f, g)
+%%   @result{} 1
+%% @end group
+%% @end example
+%%
+%% Note: two symfuns are equal if they have the same formula @emph{and}
+%% same arguments:
+%% @example
+%% @group
+%% syms x y
+%% f(x) = x + 1;
+%% g(x, y) = x + 1;
+%% isequaln(f, g)
+%%   @result{} 0
+%% @end group
+%% @end example
+%%
+%% Note: isequaln considers NaN's to be equal:
+%% @example
+%% @group
+%% syms x y
+%% f(x) = nan;
+%% g(x) = nan;
+%% isequaln(f, g)
+%%   @result{} 1
+%% @end group
+%% @end example
+%%
+%% @seealso{@@symfun/isequal, @@sym/isequal, @@symfun/formula, @@symfun/argnames}
+%% @end defmethod
+
+function t = isequaln(x, y, varargin)
+
+  if (nargin <= 1)
+    print_usage ();
+  end
+
+  t = isequaln(formula(x), formula(y)) && isequal(argnames(x), argnames(y));
+
+  if nargin >= 3 && t
+    t = t && isequaln(x, varargin{:});
+  end
+
+end
+
+%!error isequaln (symfun('x + 1', x))
+
+%!test
+%! syms x y
+%! f(x) = 2*x;
+%! g(x) = 2*x;
+%! assert (isequaln (f, g))
+
+%!test
+%! syms x
+%! f(x) = 2*x + 1;
+%! g(x) = 2*x + 1;
+%! h(x) = 2*x + 1;
+%! assert (isequaln (f, g, h))
+
+%!test
+%! syms x
+%! f(x) = 2*x + 1;
+%! g(x) = 2*x + 1;
+%! h(x) = 2*x;
+%! assert (~ isequaln (f, g, h))
+
+%!test
+%! syms x y
+%! f(x) = 2*x;
+%! g(x, y) = 2*x;
+%! assert (~ isequaln (f, g))
+
+%!test
+%! syms x y
+%! f(x) = symfun(nan, x);
+%! g(x) = symfun(nan, x);
+%! assert (isequaln (f, g))
+
+%!test
+%! syms x y
+%! f(x) = symfun(nan, x);
+%! g(x, y) = symfun(nan, x);
+%! assert (~ isequaln (f, g))