function C = twobytwoarraymult(A,B)
   %either A and B should be 2x2 matrices. either or both can be a 2x2xn matrix array, 
   %but if both are arrays, they must have the same n.  Output 
   %will be matrix multiplication of 2x2 matrices along 3rd dimentsion in A and B. 
   %either A or B will be broadcast in 3rd dimension if it is only a single matrix, 
   %otherwise it needs to be the same size as A.
   %will work for higher dimensions than three. the : will recast them as 3D arrays for 
   %the multiply, and C will be returned with the intended multidimensional size.
    
   
   if (ndims(A)>=ndims(B))
    C = zeros(size(A));
  else
    C = zeros(size(B));
  end
  
  C(1,1,:) = A(1,1,:).*B(1,1,:) + A(1,2,:).*B(2,1,:);
  C(1,2,:) = A(1,1,:).*B(1,2,:) + A(1,2,:).*B(2,2,:);
  C(2,1,:) = A(2,1,:).*B(1,1,:) + A(2,2,:).*B(2,1,:);
  C(2,2,:) = A(2,1,:).*B(1,2,:) + A(2,2,:).*B(2,2,:);
end