RMSD D root-mean-square coordinate difference.2 DISTANCE GEOMETRY: THEORY, ALGORITHMS, AND CHEMICAL APPLICATIONS which is just the symmetric part of their geometric product ab. Thus it is natural to define the outer product of two vectors as the antisymmetric part of their geometric product, i.e., a ^b D 1 2 ab ba 4 à 2 D e 1 e 2 e 3 2 D e 1 e 2 e 3 e 3 e 2 e 1 D e 1 e 2 e 2 3 e 2 e 1 D e 1 e 2 2 e 1 D e 2 1 D 1 8 a ^ b ^c D a ^b ^c D a ^b ^c 10 a ž b ^c D 1 2 a b ^c b ^c a D a ž b c a ž c b 11(and similar identities involving Ãe 3 e 1 and Ãe 2 e 3 ), we find thatMore generally, multiplication by the unit pseudo-scalar à maps vectors (bivectors) to their duals, which lie in the planes (lines) perpendicular to them, and have the same magnitudes.Let us now consider Gibbs' triple product, which is a scalar equal to the signed volume of the parallelopiped spanned by the three vectors. Using the fact that pseudo-scalars commute with everything in the algebra: a ž b ð c D 1 2 aà b ^c C à b ^c a D à 4 abc acb C bca cba D à a ^b ^c