@double/adjoint: Add new function.

Fixes gnu-octave#1049.

* inst/@double/adjoint.m: New file.
* INDEX: Adjust accordingly.
* NEWS: Adjust accordingly.

INDEX

@@ -25,6 +25,7 @@ Functions
  lambertw
  poly2sym
 Double-precision numerical functions
+ @double/adjoint
  @double/bernoulli
  @double/chebyshevT
  @double/chebyshevU

NEWS

@@ -1,6 +1,11 @@
 octsympy 3.0.0+
 ===============
 
+  * New `@double` numerical functions; these are wrappers around SymPy,
+    so they are slower than native floating-point implementations.
+
+          adjoint
+
 
 
 octsympy 3.0.0 (2022-07-05)

inst/@double/adjoint.m

@@ -0,0 +1,86 @@
+%% Copyright (C) 2022 Alex Vong
+%%
+%% 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 <https://www.gnu.org/licenses/>.
+
+%% -*- texinfo -*-
+%% @documentencoding UTF-8
+%% @defun adjoint (@var{M})
+%% Numerical Classical Adjoint / Adjugate of a square matrix.
+%%
+%% @strong{Note on Terminology}: This function computes the
+%% ``Classical Adjoint'' / Adjugate of @var{M}. For the Conjugate Transpose /
+%% Hermitian adjoint (which is commonly referred to as the ``Adjoint'' in
+%% modern usage), @pxref{@@double/ctranspose}.
+%%
+%% Example:
+%% @example
+%% @group
+%% M = [-3 2 -5; -1 0 -2; 3 -4 1];
+%% A = adjoint (M)
+%%   @result{} A =
+%%        -8   18   -4
+%%        -5   12   -1
+%%         4   -6    2
+%% @end group
+%% @end example
+%%
+%% And note the following equalities involving the Classical Adjoint @code{A}:
+%% @example
+%% @group
+%% M * A
+%%   @result{} ans =
+%%       -6   0   0
+%%        0  -6   0
+%%        0   0  -6
+%% @end group
+%%
+%% @group
+%% A * M
+%%   @result{} ans =
+%%       -6   0   0
+%%        0  -6   0
+%%        0   0  -6
+%% @end group
+%%
+%% @group
+%% det (M) * eye (3)
+%%   @result{} ans =
+%%     Diagonal Matrix
+%%
+%%       -6   0   0
+%%        0  -6   0
+%%        0   0  -6
+%% @end group
+%% @end example
+%% @seealso{@@sym/adjoint}
+%% @end defun
+
+%% Reference: https://en.wikipedia.org/wiki/Adjugate_matrix
+
+
+function A = adjoint (M)
+  A = double (adjoint (vpa (M, 16)));
+end
+
+
+%!test
+%! M = [1 2; 3 4];
+%! A = [4 -2; -3 1];
+%! assert (isequal (adjoint (M), A));
+
+%!test
+%! assert (isequal (adjoint (42), 1));