--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/scripts/miscellaneous/mustBeInteger.m	Sun Jan 19 10:07:30 2020 +0900
@@ -0,0 +1,58 @@
+########################################################################
+##
+## Copyright (C) 2019-2020 The Octave Project Developers
+##
+## See the file COPYRIGHT.md in the top-level directory of this
+## distribution or <https://octave.org/copyright/>.
+##
+## This file is part of Octave.
+##
+## Octave 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.
+##
+## Octave 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 Octave; see the file COPYING.  If not, see
+## <https://www.gnu.org/licenses/>.
+##
+########################################################################
+
+## -*- texinfo -*-
+## @deftypefn {} {@var{x} =} mustBeInteger (@var{x})
+##
+## Requires that input @var{x} is integer-valued (but not necessarily
+## integer-typed).
+##
+## Raises an error if any element of the input @var{x} is not a finite,
+## real, integer-valued numeric value, as determined by various checks.
+##
+## @end deftypefn
+
+function x = mustBeInteger (x)
+  if isinteger (x) || islogical (x)
+    return
+  endif
+  but = [];
+  if ! isnumeric (x)
+    but = sprintf ("it was non-numeric (got a %s)", class (x));
+  elseif any (! isfinite (x))
+    but = "there were Inf values";
+  elseif ! isreal (x)
+    but = "it was complex";
+  elseif ! all (floor (x) == x)
+    but = "it had fractional values in some elements";
+  end
+  if ! isempty (but)
+    label = inputname (1);
+    if isempty (label)
+      label = "input";
+    endif
+    error ("%s must be integer-valued; but %s", label, but);
+  endif
+endfunction