/usr/share/octave/packages/nurbs-1.3.13/nrbreverse.m is in octave-nurbs 1.3.13-4.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 | function nrb = nrbreverse(nrb, idir)
%
% NRBREVERSE: Reverse the evaluation directions of a NURBS geometry.
%
% Calling Sequence:
%
% rnrb = nrbreverse(nrb);
% rnrb = nrbreverse(nrb, idir);
%
% INPUT:
%
% nrb : NURBS data structure, see nrbmak.
% idir : vector of directions to reverse.
%
% OUTPUT:
%
% rnrb : Reversed NURBS.
%
% Description:
%
% Utility function to reverse the evaluation direction of a NURBS
% curve or surface.
%
% Copyright (C) 2000 Mark Spink
% Copyright (C) 2013 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 3 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/>.
if (nargin > 2)
error('Incorrect number of input arguments');
end
if (iscell(nrb.knots))
% reverse a NURBS surface or volume
ndim = numel (nrb.knots);
if (nargin == 1 || isempty (idir))
idir = 1:ndim;
end
for ii = idir
nrb.knots{ii} = sort (nrb.knots{ii}(end) - nrb.knots{ii});
nrb.coefs = flipdim (nrb.coefs, ii+1);
end
else
% reverse a NURBS curve
nrb.knots = sort (nrb.knots(end) - nrb.knots);
nrb.coefs = fliplr (nrb.coefs);
end
end
%!demo
%! pnts = [0.5 1.5 3.0 7.5 8.5;
%! 3.0 5.5 1.5 4.0 4.5;
%! 0.0 0.0 0.0 0.0 0.0];
%! crv1 = nrbmak(pnts,[0 0 0 1/2 3/4 1 1 1]);
%! crv2 = nrbreverse(crv1);
%! fprintf('Knots of the original curve\n')
%! disp(crv1.knots)
%! fprintf('Knots of the reversed curve\n')
%! disp(crv2.knots)
%! fprintf('Control points of the original curve\n')
%! disp(crv1.coefs(1:2,:))
%! fprintf('Control points of the reversed curve\n')
%! disp(crv2.coefs(1:2,:))
%! nrbplot(crv1,100)
%! hold on
%! nrbplot(crv2,100)
%! title('The curve and its reverse are the same')
%! hold off
%!test
%! srf = nrbrevolve(nrbline([1 0],[2 0]), [0 0 0], [0 0 1], pi/2);
%! srf = nrbkntins (srf, {0.3, 0.6});
%! srf2 = nrbreverse (srf);
%! assert (srf.knots, cellfun(@(x) sort(1-x), srf2.knots, 'UniformOutput', false), 1e-15)
%! assert (srf.coefs, srf2.coefs(:,end:-1:1,end:-1:1))
%!test
%! srf = nrbrevolve(nrbline([1 0],[2 0]), [0 0 0], [0 0 1], pi/2);
%! srf = nrbkntins (srf, {0.3, 0.6});
%! srf2 = nrbreverse (srf, 1);
%! knt{1} = sort(1-srf2.knots{1}); knt{2} = srf2.knots{2};
%! assert (srf.knots, knt, 1e-15)
%! assert (srf.coefs, srf2.coefs(:,end:-1:1,:))
%! srf2 = nrbreverse (srf, 2);
%! knt{1} = srf2.knots{1}; knt{2} = sort(1-srf2.knots{2});
%! assert (srf.knots, knt, 1e-15)
%! assert (srf.coefs, srf2.coefs(:,:,end:-1:1))
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