1## Copyright (C) 2021 David Legland
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27
28function c = vectorCross3d(a,b)
29%VECTORCROSS3D Vector cross product faster than inbuilt MATLAB cross.
30%
31%   C = vectorCross3d(A, B)
32%   returns the cross product of the 3D vectors A and B, that is:
33%       C = A x B
34%   A and B must be N-by-3 element vectors. If either A or B is a 1-by-3
35%   row vector, the result C will have the size of the other input and will
36%   be the  concatenation of each row's cross product.
37%
38%   Example
39%     v1 = [2 0 0];
40%     v2 = [0 3 0];
41%     vectorCross3d(v1, v2)
42%     ans =
43%         0   0   6
44%
45%
46%   Class support for inputs A,B:
47%      float: double, single
48%
49%   See also DOT.
50
51%   Sven Holcombe
52
53% needed_colons = max([3, length(size(a)), length(size(b))]) - 3;
54% tmp_colon = {':'};
55% clnSet = tmp_colon(ones(1, needed_colons));
56%
57% c = bsxfun(@times, a(:,[2 3 1],clnSet{:}), b(:,[3 1 2],clnSet{:})) - ...
58%     bsxfun(@times, b(:,[2 3 1],clnSet{:}), a(:,[3 1 2],clnSet{:}));
59
60% deprecation warning
61warning('geom3d:deprecated', ...
62    [mfilename ' is deprecated, use ''crossProduct3d'' instead']);
63
64sza = size(a);
65szb = size(b);
66
67% Initialise c to the size of a or b, whichever has more dimensions. If
68% they have the same dimensions, initialise to the larger of the two
69switch sign(numel(sza) - numel(szb))
70    case 1
71        c = zeros(sza);
72    case -1
73        c = zeros(szb);
74    otherwise
75        c = zeros(max(sza, szb));
76end
77
78c(:) =  bsxfun(@times, a(:,[2 3 1],:), b(:,[3 1 2],:)) - ...
79        bsxfun(@times, b(:,[2 3 1],:), a(:,[3 1 2],:));
80