crossProduct3d

CROSSPRODUCT3D Vector cross product faster than inbuilt MATLAB cross.

   C = crossProduct3d(A, B) 
   returns the cross product of the two 3D vectors A and B, that is: 
       C = A x B
   A and B must be N-by-3 element vectors. If either A or B is a 1-by-3
   row vector, the result C will have the size of the other input and will
   be the  concatenation of each row's cross product. 

   Example
     v1 = [2 0 0];
     v2 = [0 3 0];
     crossProduct3d(v1, v2)
     ans =
         0   0   6


   Class support for inputs A,B:
      float: double, single

   See also DOT.

0001 function c = crossProduct3d(a,b)
0002 %CROSSPRODUCT3D Vector cross product faster than inbuilt MATLAB cross.
0003 %
0004 %   C = crossProduct3d(A, B)
0005 %   returns the cross product of the two 3D vectors A and B, that is:
0006 %       C = A x B
0007 %   A and B must be N-by-3 element vectors. If either A or B is a 1-by-3
0008 %   row vector, the result C will have the size of the other input and will
0009 %   be the  concatenation of each row's cross product.
0010 %
0011 %   Example
0012 %     v1 = [2 0 0];
0013 %     v2 = [0 3 0];
0014 %     crossProduct3d(v1, v2)
0015 %     ans =
0016 %         0   0   6
0017 %
0018 %
0019 %   Class support for inputs A,B:
0020 %      float: double, single
0021 %
0022 %   See also DOT.
0023 
0024 %   Sven Holcombe
0025 
0026 % HISTORY
0027 % 2017-11-24 rename from vectorCross3d to crossProduct3d
0028 
0029 % size of inputs
0030 sizeA = size(a);
0031 sizeB = size(b);
0032 
0033 % Initialise c to the size of a or b, whichever has more dimensions. If
0034 % they have the same dimensions, initialise to the larger of the two
0035 switch sign(numel(sizeA) - numel(sizeB))
0036     case 1
0037         c = zeros(sizeA);
0038     case -1
0039         c = zeros(sizeB);
0040     otherwise
0041         c = zeros(max(sizeA, sizeB));
0042 end
0043 
0044 c(:) = bsxfun(@times, a(:,[2 3 1],:), b(:,[3 1 2],:)) - ...
0045        bsxfun(@times, b(:,[2 3 1],:), a(:,[3 1 2],:));