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+## Copyright (C) 2008-2012 David Bateman
+##
+## 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
+## <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {@var{yi} =} interp1q (@var{x}, @var{y}, @var{xi})
+## One-dimensional linear interpolation without error checking.
+## Interpolates @var{y}, defined at the points @var{x}, at the points
+## @var{xi}.  The sample points @var{x} must be a strictly monotonically
+## increasing column vector.  If @var{y} is an array, treat the columns
+## of @var{y} separately.  If @var{y} is a vector, it must be a column
+## vector of the same length as @var{x}.
+##
+## Values of @var{xi} beyond the endpoints of the interpolation result
+## in NA being returned.
+##
+## Note that the error checking is only a significant portion of the
+## execution time of this @code{interp1} if the size of the input arguments
+## is relatively small.  Therefore, the benefit of using @code{interp1q}
+## is relatively small.
+## @seealso{interp1}
+## @end deftypefn
+
+function yi = interp1q (x, y, xi)
+  x = x(:);
+  nx = size (x, 1);
+  szy = size (y);
+  y = y(:,:);
+  [ny, nc] = size (y);
+  szx = size (xi);
+  xi = xi (:);
+  dy = diff (y);
+  dx = diff (x);
+  idx = lookup (x, xi, "lr");
+  s = (xi - x (idx)) ./ dx (idx);
+  yi = bsxfun (@times, s, dy(idx,:)) + y(idx,:);
+  range = xi < x(1) | !(xi <= x(nx));
+  yi(range,:) = NA;
+  if (length (szx) == 2 && any (szx == 1))
+    yi = reshape (yi, [max(szx), szy(2:end)]);
+  else
+    yi = reshape (yi, [szx, szy(2:end)]);
+  endif
+endfunction
+
+%!shared xp, yp, xi, yi
+%! xp=[0:2:10].';      yp = sin(2*pi*xp/5);
+%! xi = [-1; 0; 2.2; 4; 6.6; 10; 11];
+%! yi = interp1 (xp,yp,xi);
+%!assert (interp1q(xp, yp, [min(xp)-1; max(xp)+1]), [NA; NA]);
+%!assert (interp1q(xp,yp,xp), yp, 100*eps);
+%!assert (isempty(interp1q(xp,yp,[])));
+%!assert (interp1q(xp,yp,xi), yi);
+%!assert (interp1q(xp,[yp,yp],xi), [yi, yi]);
+%!assert (interp1q(xp,yp,[xi,xi]), [yi, yi]);
+%!assert (interp1q(xp,[yp,yp],[xi,xi]), cat (3, [yi, yi], [yi, yi]));