/usr/share/octave/packages/nurbs-1.3.13/findspan.m is in octave-nurbs 1.3.13-4.
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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 | function s = findspan(n,p,u,U)
% FINDSPAN Find the span of a B-Spline knot vector at a parametric point
%
% Calling Sequence:
%
% s = findspan(n,p,u,U)
%
% INPUT:
%
% n - number of control points - 1
% p - spline degree
% u - parametric point
% U - knot sequence
%
% OUTPUT:
%
% s - knot span index
%
% Modification of Algorithm A2.1 from 'The NURBS BOOK' pg68
%
% Copyright (C) 2010 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 (max(u(:))>U(end) || min(u(:))<U(1))
error('Some value is outside the knot span')
end
s = zeros(size(u));
for j = 1:numel(u)
if (u(j)==U(n+2)), s(j)=n; continue, end
s(j) = find(u(j) >= U,1,'last')-1;
end
end
%!test
%! n = 3;
%! U = [0 0 0 1/2 1 1 1];
%! p = 2;
%! u = linspace(0, 1, 10);
%! s = findspan (n, p, u, U);
%! assert (s, [2*ones(1, 5) 3*ones(1, 5)]);
%!test
%! p = 2; m = 7; n = m - p - 1;
%! U = [zeros(1,p) linspace(0,1,m+1-2*p) ones(1,p)];
%! u = [ 0 0.11880 0.55118 0.93141 0.40068 0.35492 0.44392 0.88360 0.35414 0.92186 0.83085 1];
%! s = [2 2 3 4 3 3 3 4 3 4 4 4];
%! assert (findspan (n, p, u, U), s, 1e-10);
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