Duals
Every object in projective geometric algebra has two duals derived from the metric tensor, called the metric dual and metric antidual.
Dual
The metric dual or just "dual" of an object $$\mathbf u$$ is denoted by $$\mathbf u^\unicode["segoe ui symbol"]{x2605}$$ and defined as
- $$\mathbf u^\unicode["segoe ui symbol"]{x2605} = \overline{\mathbf{Gu}}$$ ,
where $$\mathbf G$$ is the extended metric tensor. In projective geometric algebra, this dual is also called the bulk dual because it is the complement of the bulk components, as expressed by
- $$\mathbf u^\unicode["segoe ui symbol"]{x2605} = \overline{\mathbf u_\unicode{x25CF}}$$ .
The bulk dual satisfies the following identity based on the geometric product:
- $$\mathbf u^\unicode["segoe ui symbol"]{x2605} = \tilde{\mathbf u} \mathbin{\unicode{x27D1}} {\large\unicode{x1D7D9}}$$ .
Antidual
The metric antidual or just "antidual" of an object $$\mathbf u$$ is denoted by $$\mathbf u^\unicode["segoe ui symbol"]{x2606}$$ and defined as
- $$\mathbf u^\unicode["segoe ui symbol"]{x2606} = \overline{\mathbb G \mathbf u}$$ ,
where $$\mathbb G$$ is the extended antimetric tensor. In projective geometric algebra, this dual is also called the weight dual because it is the complement of the weight components, as expressed by
- $$\mathbf u^\unicode["segoe ui symbol"]{x2606} = \overline{\mathbf u_\unicode{x25CB}}$$ .
The weight dual satisfies the following identity based on the geometric antiproduct:
- $$\mathbf u^\unicode["segoe ui symbol"]{x2606} = \smash{\mathbf{\underset{\Large\unicode{x7E}}{u}}} \mathbin{\unicode{x27C7}} \mathbf 1$$ .