--- a/scripts/set/setdiff.m	Thu Jul 11 15:05:30 2019 -0700
+++ b/scripts/set/setdiff.m	Thu Jul 11 15:29:38 2019 -0700
@@ -20,6 +20,7 @@
 ## -*- texinfo -*-
 ## @deftypefn  {} {@var{c} =} setdiff (@var{a}, @var{b})
 ## @deftypefnx {} {@var{c} =} setdiff (@var{a}, @var{b}, "rows")
+## @deftypefnx {} {@var{c} =} setdiff (@dots{}, "legacy")
 ## @deftypefnx {} {[@var{c}, @var{ia}] =} setdiff (@dots{})
 ## Return the unique elements in @var{a} that are not in @var{b} sorted in
 ## ascending order.
@@ -33,6 +34,10 @@
 ##
 ## If requested, return the index vector @var{ia} such that
 ## @code{@var{c} = @var{a}(@var{ia})}.
+##
+## Programming Note: The input flag @qcode{"legacy"} changes the algorithm
+## to be compatible with @sc{matlab} releases prior to R2012b.
+##
 ## @seealso{unique, union, intersect, setxor, ismember}
 ## @end deftypefn
 
@@ -41,24 +46,30 @@
 
 function [c, ia] = setdiff (a, b, varargin)
 
-  if (nargin < 2 || nargin > 3)
+  if (nargin < 2 || nargin > 4)
     print_usage ();
   endif
 
   [a, b] = validsetargs ("setdiff", a, b, varargin{:});
 
-  by_rows = nargin == 3;
-  isrowvec = isrow (a);
+  by_rows = any (strcmp ("rows", varargin));
+  optlegacy = any (strcmp ("legacy", varargin));
+
+  if (optlegacy)
+    isrowvec = ! iscolumn (a) || ! iscolumn (b);
+  else
+    isrowvec = isrow (a);
+  endif
 
   if (by_rows)
     if (nargout > 1)
-      [c, ia] = unique (a, "rows");
+      [c, ia] = unique (a, varargin{:});
     else
-      c = unique (a, "rows");
+      c = unique (a, varargin{:});
     endif
     if (! isempty (c) && ! isempty (b))
       ## Form A and B into combined set.
-      b = unique (b, "rows");
+      b = unique (b, varargin{:});
       [tmp, idx] = sortrows ([c; b]);
       ## Eliminate those elements of A that are the same as in B.
       dups = find (all (tmp(1:end-1,:) == tmp(2:end,:), 2));
@@ -69,9 +80,9 @@
     endif
   else
     if (nargout > 1)
-      [c, ia] = unique (a);
+      [c, ia] = unique (a, varargin{:});
     else
-      c = unique (a);
+      c = unique (a, varargin{:});
     endif
     if (! isempty (c) && ! isempty (b))
       ## Form a and b into combined set.
@@ -84,15 +95,18 @@
         dups = find (tmp(1:end-1) == tmp(2:end));
       endif
       c(idx(dups)) = [];
-      if (nargout > 1)
-        ia(idx(dups)) = [];
-      endif
       ## Reshape if necessary for Matlab compatibility.
       if (isrowvec)
         c = c(:).';
       else
         c = c(:);
       endif
+      if (nargout > 1)
+        ia(idx(dups)) = [];
+        if (optlegacy && isrowvec)
+          ia = ia(:).';
+        endif
+      endif
     endif
   endif
 
@@ -126,3 +140,36 @@
 %! a = rand (3,3,3);
 %! b = a(1);
 %! assert (setdiff (a, b), sort (a(2:end)'));
+
+## Test "rows" compatibility
+%!test
+%! a = [7 9 7; 0 0 0; 7 9 7; 5 5 5; 1 4 5];
+%! b = [0 0 0; 5 5 5];
+%! [c, ia] = setdiff (a, b, "rows");
+%! assert (c, [1, 4 ,5; 7, 9 7]);
+%! assert (ia, [5; 1]);
+
+## Test "legacy" option
+%!test
+%! a = [3, 6, 2, 1, 5, 1, 1];
+%! b = [2, 4, 6];
+%! [c, ia] = setdiff (a, b);
+%! assert (c, [1, 3, 5]);
+%! assert (ia, [4; 1; 5]);
+%! [c, ia] = setdiff (a, b, "legacy");
+%! assert (c, [1, 3, 5]);
+%! assert (ia, [7, 1, 5]);
+
+## "legacy" + "rows" compatibility
+%!test
+%! a = [7 9 7; 0 0 0; 7 9 7; 5 5 5; 1 4 5];
+%! b = [0 0 0; 5 5 5];
+%! [c, ia] = setdiff (a, b, "rows", "legacy");
+%! assert (c, [1, 4 ,5; 7, 9 7]);
+%! assert (ia, [5; 3]);
+
+## Output orientation with "legacy" option 
+%!assert (size (setdiff ([1:5], [2:3], "legacy")), [1, 3])
+%!assert (size (setdiff ([1:5]', [2:3], "legacy")), [1, 3])
+%!assert (size (setdiff ([1:5], [2:3]', "legacy")), [1, 3])
+%!assert (size (setdiff ([1:5]', [2:3]', "legacy")), [3, 1])