Exterior algebra

cosmos 6th November 2017 at 4:05pm
Algebra (algebraic structure) Exterior calculus Tensor algebra

The exterior algebra is a quotient of the Tensor algebra, with product the Wedge product

It can be defined as V=T(V)/I(V)\wedge^* V = T(V)/I(V)

where T(V)T(V) is the Tensor algebra of VV and I(V)I(V) is the Ideal generated by elements of the form vvv \otimes v where vVv \in V. So I(V)I ( V ) consists of all sums of multiples by T(V)T ( V ) on the left and right of these generators. We can also see I(V)I(V) as the kernel of a certain projection map related to Permutations (see wave-notebook..)

Equivalently, we can define kV\wedge^k V (called exterior power) to be the Vector subspace of kV\otimes^k V on which the Symmetric group acts antisymmetrically (see wave-notebook..).

See here and wave-notebook.

If v1,...,vnv_1,...,v_n is a basis for VV, then {vi1vi2...vik:1i1<i2<...ikn}\{v_{i_1} \wedge v_{i_2} \wedge ... \wedge v_{i_k} : 1 \leq i_1 < i_2 < ... i_k \leq n\} is a basis for kV\wedge^k V. Hence the dimension of kV\wedge^k V is (nk)\binom{n}{k}. It is an associative supercommutative graded R\mathbb{R}-algebra

– The wedge product, exterior power and exterior algebra can be defined for Vector bundles too. The elements of an exterior power of vector bundles are called Exterior forms