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Geometric algebra
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=== Table of models === Note in this list that {{tmath|1= p }} and {{tmath|1= q }} can be swapped and the same name applies; for example, with ''relatively'' little change occurring, see [[sign convention]]. For example, <math>\mathcal{G}(3, 1, 0)</math> and <math>\mathcal{G}(1, 3, 0)</math> are ''both'' referred to as Spacetime Algebra.{{sfn|ps=|Wu|2022}} {| class="wikitable" |+ ! Name ! Signature ! Blades, e.g., oriented geometric objects that algebra can represent ! Rotors, e.g., [[Orientation (vector space)|orientation]]-preserving transformations that the algebra can represent ! Notes |- | Vectorspace GA, VGA [[Algebra of physical space|Algebra of Physical Space]], APS | <math>\mathcal{G}(3,0,0)</math> | Planes and lines through the origin | Rotations, e.g. <math>\mathrm{SO} (3)</math> | First GA to be discovered by William Clifford |- | Projective GA, PGA, Rigid GA, RGA, [[Plane-based Geometric Algebra|Plane-based GA]] | <math>\mathcal{G}(3,0,1)</math> | Planes, lines, and points anywhere in space | Rotations and translations, e.g., [[Rigid transformation|rigid motions]], <math>\mathrm{SE}(3)</math> aka <math>\mathrm{SO}(3,0,1)</math> | Slight modifications to the signature allow for the modelling of hyperbolic and elliptic space, see main article. Cannot model the entire "projective" group. |- | [[Spacetime algebra|Spacetime Algebra]], STA | <math>\mathcal{G}(3,1,0)</math> | Volumes, planes and lines through the origin in spacetime | Rotations and spacetime boosts, e.g. {{tmath|1= \mathrm{SO}(3,1) }}, the [[Lorentz group]] | Basis for [[Gauge theory gravity|Gauge Theory Gravity]]. |- | Spacetime Algebra Projectivized,{{sfn|ps=|Sokolov|2013}} STAP | <math>\mathcal{G}(3,1,1)</math> | Volumes, planes, lines, and points (events) in spacetime | Rotations, translations, and spacetime boosts ([[Poincaré group|Poincare group]]) | |- | [[Conformal geometric algebra|Conformal GA]], CGA | <math>\mathcal{G}(4,1,0)</math> | Spheres, circles, point pairs (or dipoles), round points, flat points, lines, and planes anywhere in space | Transformations of space that preserve angles ([[Conformal group]] {{tmath|1= \mathrm{SO}(4,1) }}) | |- | Conformal Spacetime Algebra,{{sfn|ps=|Lasenby|2004}} CSTA | <math>\mathcal{G}(4,2,0)</math> | Spheres, circles, planes, lines, light-cones, trajectories of objects with constant acceleration, all in spacetime | Conformal transformations of spacetime, e.g. transformations that preserve [[rapidity]] along arclengths through spacetime | Related to [[Twistor theory]]. |- | Mother Algebra{{sfn|ps=|Dorst|2016}} | <math>\mathcal{G}(3,3,0)</math> | Unknown | Projective group | |- | GA for Conics, GAC Quadric Conformal 2D GA QC2GA{{sfn|ps=|Perwass|2009}}{{sfn|ps=|Hrdina|Návrat|Vašík|2018}} | <math>\mathcal{G}(5,3,0)</math> | Points, point pair/triple/quadruple, Conic, Pencil of up to 6 independent conics. | Reflections, translations, rotations, dilations, others | Conics can be created from control points and pencils of conics. |- | Quadric Conformal GA, QCGA{{sfn|ps=|Breuils|Fuchs|Hitzer|Nozick|2019}} | <math>\mathcal{G}(9,6,0)</math> | Points, tuples of up to 8 points, quadric surfaces, conics, conics on quadratic surfaces (such as [[Spherical conic]]), pencils of up to 9 quadric surfaces. | Reflections, translations, rotations, dilations, others | Quadric surfaces can be created from control points and their surface normals can be determined. |- | Double Conformal Geometric Algebra (DCGA){{sfn|ps=|Easter|Hitzer|2017}} | <math>\mathcal{G}(8,2,0)</math> | Points, Darboux Cyclides, quadrics surfaces | Reflections, translations, rotations, dilations, others | Uses bivectors of two independent CGA basis to represents 5×5 symmetric "matrices" of 15 unique coefficients. This is at the cost of the ability to perform intersections and construction by points. |- |}
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