function d = det3(A)% det3 - 3x3 determinant%%   d = det3(A);%%   A is a [3 3 n] matrix, d is a vector of size d where%   d(i)=det(A(:,:,i)).%%   It computes explicitely the det by expanding along the 1st columns 2x2%   determinant. Faster than recursive loops.%%   Note: works also for 2x2 det.%   Note: for higher order det, use loop%%   Copyright (c) 2008 Gabriel Peyreif size(A,1)==2 && size(A,2)==2    %% 2x2 Det %%    d = A(1,1,:).*A(2,2,:) - A(1,2,:).*A(2,1,:);elseif size(A,1)==3 && size(A,2)==3    %% 3x3 Det %%    d = A(1,1,:).*( A(2,2,:).*A(3,3,:) - A(2,3,:).*A(3,2,:) ) - ...        A(1,2,:).*( A(2,1,:).*A(3,3,:) - A(2,3,:).*A(3,1,:) ) + ...        A(1,3,:).*( A(2,1,:).*A(3,2,:) - A(2,2,:).*A(3,1,:) );else    n = size(A,3);    d = zeros(n,1);    for i=1:n        d(i) = det(A(:,:,i));    endendd = d(:);