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diff --git a/octave_packages/nurbs-1.3.6/kntrefine.m b/octave_packages/nurbs-1.3.6/kntrefine.m
new file mode 100644
index 0000000..d1f9d63
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+++ b/octave_packages/nurbs-1.3.6/kntrefine.m
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+% KNTREFINE: Refine a given knot vector by dividing each interval uniformly,
+%             maintaining the continuity in previously existing knots.
+%
+%   [rknots]                  = kntrefine (knots, n_sub, degree, regularity)
+%   [rknots, zeta]            = kntrefine (knots, n_sub, degree, regularity)
+%   [rknots, zeta, new_knots] = kntrefine (knots, n_sub, degree, regularity)
+%
+% INPUT:
+%
+%     knots:      initial knot vector.
+%     n_sub:      number of new knots to be added in each interval.
+%     degree:     polynomial degree of the refined knot vector
+%     regularity: maximum global regularity 
+%
+% OUTPUT:
+%
+%     rknots:    refined knot vector
+%     zeta:      refined knot vector without repetitions
+%     new_knots: new knots, to apply the knot insertion
+%
+% The regularity at the new inserted knots is the one given by the user.
+% At previously existing knots, the regularity is the minimum
+%  between the previous regularity, and the one given by the user.
+%  This ensures optimal convergence rates in the context of IGA.
+%
+% Copyright (C) 2010 Carlo de Falco, Rafael Vazquez
+%
+%    This program 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 2 of the License, or
+%    (at your option) any later version.
+
+%    This program 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 program.  If not, see <http://www.gnu.org/licenses/>.
+
+function varargout = kntrefine (knots, n_sub, degree, regularity)
+
+  if (iscell(knots))
+    if (numel(n_sub)~=numel(degree) || numel(n_sub)~=numel(regularity) || ...
+        numel(n_sub)~=numel(knots))
+      error('kntrefine: n_sub, degree and regularity must have the same length as the number of knot vectors')
+    end
+    aux_knots = knots;
+  else
+    if (numel(n_sub)~=numel(degree) || numel(n_sub)~=numel(regularity) || ...
+        numel(n_sub)~=1)
+      error('kntrefine: n_sub, degree and regularity must have the same length as the number of knot vectors')
+    end
+    aux_knots = {knots};
+  end
+
+  if (nargout == 3)
+    for idim = 1:numel(n_sub)
+      if (degree(idim)+1 ~= sum (aux_knots{idim}==aux_knots{idim}(1)))
+        error ('kntrefine: new_knots is only computed when the degree is maintained');
+      end
+    end
+    for idim = 1:numel(n_sub)
+      min_mult     = degree(idim) - regularity(idim);
+      z            = unique (aux_knots{idim});
+      nz           = numel (z);
+      deg          = sum (aux_knots{idim} == z(1)) - 1;
+      rknots{idim} = z(ones(1, degree(idim)+1));
+      new_knots{idim} = [];
+ 
+      for ik = 2:nz
+        insk = linspace (z(ik-1), z(ik), n_sub(idim) + 2);
+        insk = vec (repmat (insk(2:end-1), min_mult, 1))';
+        old_mult = sum (aux_knots{idim} == z(ik));
+        mult = max (min_mult, degree(idim) - deg + old_mult);
+        rknots{idim} = [rknots{idim}, insk, z(ik*ones(1, mult))];
+        new_knots{idim} = [new_knots{idim}, insk, z(ik*ones(1, mult-old_mult))];
+      end
+      zeta{idim} = unique (rknots{idim});
+    end
+    if (~iscell(knots))
+      rknots = rknots{1};
+      zeta = zeta{1};
+      new_knots = new_knots{1};
+    end
+    varargout{1} = rknots;
+    varargout{2} = zeta;
+    varargout{3} = new_knots;
+  else
+    for idim = 1:numel(n_sub)
+      min_mult     = degree(idim) - regularity(idim);
+      z            = unique (aux_knots{idim});
+      nz           = numel (z);
+      deg          = sum (aux_knots{idim} == z(1)) - 1;
+      rknots{idim} = z(ones(1, degree(idim)+1));
+ 
+      for ik = 2:nz
+        insk = linspace (z(ik-1), z(ik), n_sub(idim) + 2);
+        insk = vec (repmat (insk(2:end-1), min_mult, 1))';
+        old_mult = sum (aux_knots{idim} == z(ik));
+        mult = max (min_mult, degree(idim) - deg + old_mult);
+        rknots{idim} = [rknots{idim}, insk, z(ik*ones(1, mult))];
+      end
+      zeta{idim} = unique (rknots{idim});
+    end
+    if (~iscell(knots))
+      rknots = rknots{1};
+      zeta = zeta{1};
+    end
+    varargout{1} = rknots;
+    if (nargout == 2)
+      varargout{2} = zeta;
+    end
+  end
+end
+
+function v = vec (in)
+  v = in(:);
+end
+
+%!shared nrbs
+%!test
+%! knots = {[0 0 1 1] [0 0 0 1 1 1]};
+%! coefs(1,:,:) = [1 sqrt(2)/2 0; 2 sqrt(2) 0];
+%! coefs(2,:,:) = [0 sqrt(2)/2 1; 0 sqrt(2) 2];
+%! coefs(4,:,:) = [1 sqrt(2)/2 1; 1 sqrt(2)/2 1];
+%! nrbs = nrbmak (coefs, knots);
+%! nrbs = nrbkntins (nrbs, {[] [0.5 0.6 0.6]});
+%! nrbs = nrbdegelev (nrbs, [0 1]);
+%! nrbs = nrbkntins (nrbs, {[] [0.4]});
+%! rknots = kntrefine (nrbs.knots, [1 1], [1 1], [0 0]);
+%! assert (rknots{1} == [0 0 0.5 1 1]);
+%! assert (rknots{2} == [0 0 0.2 0.4 0.45 0.5 0.55 0.6 0.8 1 1]);
+%!
+%!test
+%! rknots = kntrefine (nrbs.knots, [1 1], [3 3], [0 0]);
+%! assert (rknots{1}, [0 0 0 0 0.5 0.5 0.5 1 1 1 1]);
+%! assert (rknots{2}, [0 0 0 0 0.2 0.2 0.2 0.4 0.4 0.4 0.45 0.45 0.45 0.5 0.5 0.5 0.55 0.55 0.55 0.6 0.6 0.6 0.8 0.8 0.8 1 1 1 1]);
+%!
+%!test
+%! rknots = kntrefine (nrbs.knots, [1 1], [3 3], [2 2]);
+%! assert (rknots{1}, [0 0 0 0 0.5 1 1 1 1]);
+%! assert (rknots{2}, [0 0 0 0 0.2 0.4 0.45 0.5 0.5 0.55 0.6 0.6 0.6 0.8 1 1 1 1]);
+%!
+%!test
+%! rknots = kntrefine (nrbs.knots, [1 1], [4 4], [0 0]);
+%! assert (rknots{1}, [0 0 0 0 0 0.5 0.5 0.5 0.5 1 1 1 1 1]);
+%! assert (rknots{2}, [0 0 0 0 0 0.2 0.2 0.2 0.2 0.4 0.4 0.4 0.4 0.45 0.45 0.45 0.45 0.5 0.5 0.5 0.5 0.55 0.55 0.55 0.55 0.6 0.6 0.6 0.6 0.8 0.8 0.8 0.8 1 1 1 1 1]);
+%!
+%!test
+%! rknots = kntrefine (nrbs.knots, [1 1], [4 4], [3 3]);
+%! assert (rknots{1}, [0 0 0 0 0 0.5 1 1 1 1 1]);
+%! assert (rknots{2}, [0 0 0 0 0 0.2 0.4 0.4 0.45 0.5 0.5 0.5 0.55 0.6 0.6 0.6 0.6 0.8 1 1 1 1 1]);
+%!
+%!test
+%! knots = [0 0 0 0 0.4 0.5 0.5 0.6 0.6 0.6 1 1 1 1];
+%! rknots = kntrefine (knots, 1, 4, 3);
+%! assert (rknots, [0 0 0 0 0 0.2 0.4 0.4 0.45 0.5 0.5 0.5 0.55 0.6 0.6 0.6 0.6 0.8 1 1 1 1 1]);