Geometric Algebra for Mathematicians

Total Page:16

File Type:pdf, Size:1020Kb

Geometric Algebra for Mathematicians Geometric Algebra for Mathematicians Kalle Rutanen 09.04.2013 (this is an incomplete draft) 1 Contents 1 Preface 4 1.1 Relation to other texts . 4 1.2 Acknowledgements . 6 2 Preliminaries 11 2.1 Basic definitions . 11 2.2 Vector spaces . 12 2.3 Bilinear spaces . 21 2.4 Finite-dimensional bilinear spaces . 27 2.5 Real bilinear spaces . 29 2.6 Tensor product . 32 2.7 Algebras . 33 2.8 Tensor algebra . 35 2.9 Magnitude . 35 2.10 Topological spaces . 37 2.11 Topological vector spaces . 39 2.12 Norm spaces . 40 2.13 Total derivative . 44 3 Symmetry groups 50 3.1 General linear group . 50 3.2 Scaling linear group . 51 3.3 Orthogonal linear group . 52 3.4 Conformal linear group . 55 3.5 Affine groups . 55 4 Algebraic structure 56 4.1 Clifford algebra . 56 4.2 Morphisms . 58 4.3 Inverse . 59 4.4 Grading . 60 4.5 Exterior product . 64 4.6 Blades . 70 4.7 Scalar product . 72 4.8 Contraction . 74 4.9 Interplay . 80 4.10 Span . 81 4.11 Dual . 87 4.12 Commutator product . 89 4.13 Orthogonality . 90 4.14 Magnitude . 93 4.15 Exponential and trigonometric functions . 94 2 5 Linear transformations 97 5.1 Determinant . 97 5.2 Pinors and unit-versors . 98 5.3 Spinors and rotors . 104 5.4 Projections . 105 5.5 Reflections . 105 5.6 Adjoint . 107 6 Geometric applications 107 6.1 Cramer’s rule . 108 6.2 Gram-Schmidt orthogonalization . 108 6.3 Alternating forms and determinant . 109 6.4 Reciprocal bases . 109 3 1 Preface A real vector space V allows the representation of 1-dimensional, weighted, oriented subspaces. A given vector v 2 V represents the subspace span(fvg) = fαv : α 2 Rg, called the span of v. Inside this subspace, vectors can be compared with respect to v; if w = αv, for some α 2 R, then its magnitude (relative to v) is jαj and its orientation (relative to v) is sgn(α). To compare vectors between different subspaces requires a way to measure magnitudes. This is made possible by introducing a symmetric bilinear form in V , turning V into a symmetric bilinear space. An exterior algebra on V extends V to a unital associative algebra G(V ), which allows the representation of subspaces of V as elements of G(V ). Each k-dimensional subspace of V can be represented in G(V ) as an exterior product of k vectors, and vice versa. Each element representing the same subspace in G(V ), the span of the element, can be compared to a baseline element to obtain its relative magnitude and relative orientation. A symmetric bilinear form in V induces a symmetric bilinear form in G(V ) (the scalar product), so that G(V ) also becomes a symmetric bilinear space. Given a symmetric bilinear form in G(V ), one may measure magnitudes of subspaces, and define the contraction in G(V ), which is the algebraic representation of the orthogonal complement of a subspace A ⊂ V on a subspace B ⊂ V . A Clifford algebra on V introduces a single product, the geometric product, in G(V ), which encompasses both the spanning properties required to form subspaces, and the metric properties required to measure magnitudes. A special property of this product over the more specific products is that it is associative. This brings in the structure of a unital associative algebra, which has the desirable properties of possessing a unique identity and unique inverses. Applying the geometric product in a versor product provides a structure- preserving way to perform reflections in V , which extends to orthogonal transformations in V by the Cartan-Dieudonné theorem. 1.1 Relation to other texts This paper can be thought to complement the book Geometric Algebra for Computer Science [3], which we think is an excellent exposition of the state-of-the-art in geometric algebra, both in content and writing. A mathematician, however, desires for greater succinctness and detail; we aim to provide that in this paper. Ideally, one would alternate between this paper, for increased mathematical intuition, and that book, for increased geometric intuition. The organization of this paper is inspired by the Schaum’s Outlines series. In partic- ular, we begin each section by giving the definitions without additional prose, and then follow up with a set of theorems, remarks, and examples concerning those definitions. In addition, we give many of the theorems and remarks a short summary; we hope this makes it more efficient to skip familiar parts later when recalling the subject matter. In addition to [3], we merge together ideas from several other texts on geometric algebra, notably [4] and [2]. Here we briefly summarize the key points in which we have either adopted, or diverged from, an idea. A comparison between terms in different texts is given in Table 1. Remark 1.1.1 (Coordinate-free proofs). We prove the results in Clifford algebra 4 Table 1: Comparison of terms between texts Concept This paper [4] [3] Product of k vectors Versor Versor - Product of k invertible vectors Invertible versor Invertible versor Versor Simple element of Cl(V ) k-blade simple k-vector k-blade Solutions to v ^ A = 0 Span ? Attitude Measure of size in Cl(V ) Magnitude Magnitude Weight without assuming a priviledged basis for the vectors. This reveals structure in proofs. The key theorem in this task is Theorem 4.5.14, which shows that vector-preserving homomorphisms preserve grade. Remark 1.1.2 (General form for the bilinear form). We do not assume any par- ticular form for the underlying symmetric bilinear form. This makes it explicit which theorems generalize to arbitrary symmetric bilinear forms, and which do not. In addi- tion, this reveals structure in proofs. Remark 1.1.3 (Contraction, not inner products). We adopt the definition of con- traction from [3]. This definition is different from [4] and [2]. See Section 4.8 for details. Remark 1.1.4 (Explicit notation for dual). We denote the dual of a k-blade Ak on Bl an invertible l-blade Bl by Ak . This notation is shown appropriate by Theorem 4.11.4, which says that Bl Bl span Ak = span(Ak) : (1.1.1) In addition, this makes the l-blade Bl explicit, which is important when taking duals in ∗ subspaces. We diverge from [3], which uses the notation Ak, and assumes the reader is −∗ aware of the l-blade Bl relative to which the dual is taken. The undual Ak in [3] is given −1 B by Ak l . Remark 1.1.5 (Minor corrections). To translate results between this paper and [3], it is useful to be aware of some minor errors in their text: • What they call a bilinear form is actually a symmetric bilinear form. • What they call a degenerate bilinear form is actually an indefinite non-degenerate symmetric bilinear form, so of signature (p; q; 0). • What they call a metric space is actually a norm space. • What they call a norm is correct, but only defined when the underlying symmetric bilinear form is positive-definite. These errors are minor, and in no way affect the excellent readability of [3]. 5 1.2 Acknowledgements My interest on geometric algebra grew from my interest in geometric algorithms and computer graphics. Specifically, I was led to consider the question of whether there was some good way to obtain the intersection of two affine flats. After having queried this in the then active comp.graphics.algorithms USENET newsgroup, I was replied by a knowledgeable person named Just’d’Faqs, who suggested that I take a look at geometric algebra. This got me interested in geometric algebra, but unfortunately I did not have the time to study it back then. In 2010, I started my doctoral studies on geometric algebra (although I eventually changed the subject). It is this way that I was led to my doctoral supervisor, professor Sirkka-Liisa Eriksson, and to work as an exercise assistant on her course on geometric algebra. This paper got its start during the Christmas holiday 2011, as an attempt to clarify things to myself, before the start of the geometric algebra course in Spring 2012. I found the process such a good learning experience that I decided to continue on the writing on my free time. However, it wasn’t until the end of 2012 that I would pick up on writing again, the motivation being the same geometric algebra course in Spring 2013. This paper, then, is the result of that process. I would like to thank Just’d’Faqs for guiding me to this direction, and Sirkka-Liisa Eriksson, for introducing me to the subject through her course. This paper wouldn’t exist without the excellent books of Hestenes et al. [4], Dorst et al. [3], and Doran et al. [2]; these are the texts from which I have absorbed my knowledge. 6 Table 2: Latin alphabet (small) Symbol Meaning Example a, b, c, d Vector in a vector space, 1-vector a 2 V e Exponential function eB2 f, g, h Function f(x), g ◦ h i, j Index i 2 I k, l, m Cardinality of a set, grade of a k-vector fa1; : : : ; akg, Ak n Dimension of a vector space o Avoided; resembles zero p, q, r A distinguished point limx!p f(x) = y s, t - u, v, w Vector in a vector space x, y, z Point in a topological space p, q, r Represented point in the conformal model [p] Point representative in the conformal model p 2 [p] 7 Table 3: Latin alphabet (capitals) Symbol Meaning Example Pn A, B, C Multi-vector A = k=0 Ak Ak, Bl, Cm k-vector B Basis of a vector space or of a topological space BX ⊂ TX C Closed sets of a topological space CX D, E - F Field α 2 F G, H Group I, J Index set faigi2I ⊂ V K - L Linear functions between vector spaces L(U; V ) M, N, O Neighborhood, open set Op 2 TX (p) P , Q - R Rotor S Subset, subspace S ⊂ V T Topology TX U, V , W Vector space v 2 V X, Y , Z Topological space x 2 X 8 Table 4: Greek alphabet (small) Symbol Meaning Example α, β, γ Scalar, scalar tuple α 2 F , β
Recommended publications
  • Geometric Algebra for Vector Fields Analysis and Visualization: Mathematical Settings, Overview and Applications Chantal Oberson Ausoni, Pascal Frey
    Geometric algebra for vector fields analysis and visualization: mathematical settings, overview and applications Chantal Oberson Ausoni, Pascal Frey To cite this version: Chantal Oberson Ausoni, Pascal Frey. Geometric algebra for vector fields analysis and visualization: mathematical settings, overview and applications. 2014. hal-00920544v2 HAL Id: hal-00920544 https://hal.sorbonne-universite.fr/hal-00920544v2 Preprint submitted on 18 Sep 2014 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Geometric algebra for vector field analysis and visualization: mathematical settings, overview and applications Chantal Oberson Ausoni and Pascal Frey Abstract The formal language of Clifford’s algebras is attracting an increasingly large community of mathematicians, physicists and software developers seduced by the conciseness and the efficiency of this compelling system of mathematics. This contribution will suggest how these concepts can be used to serve the purpose of scientific visualization and more specifically to reveal the general structure of complex vector fields. We will emphasize the elegance and the ubiquitous nature of the geometric algebra approach, as well as point out the computational issues at stake. 1 Introduction Nowadays, complex numerical simulations (e.g. in climate modelling, weather fore- cast, aeronautics, genomics, etc.) produce very large data sets, often several ter- abytes, that become almost impossible to process in a reasonable amount of time.
    [Show full text]
  • Quaternions and Cli Ord Geometric Algebras
    Quaternions and Cliord Geometric Algebras Robert Benjamin Easter First Draft Edition (v1) (c) copyright 2015, Robert Benjamin Easter, all rights reserved. Preface As a rst rough draft that has been put together very quickly, this book is likely to contain errata and disorganization. The references list and inline citations are very incompete, so the reader should search around for more references. I do not claim to be the inventor of any of the mathematics found here. However, some parts of this book may be considered new in some sense and were in small parts my own original research. Much of the contents was originally written by me as contributions to a web encyclopedia project just for fun, but for various reasons was inappropriate in an encyclopedic volume. I did not originally intend to write this book. This is not a dissertation, nor did its development receive any funding or proper peer review. I oer this free book to the public, such as it is, in the hope it could be helpful to an interested reader. June 19, 2015 - Robert B. Easter. (v1) [email protected] 3 Table of contents Preface . 3 List of gures . 9 1 Quaternion Algebra . 11 1.1 The Quaternion Formula . 11 1.2 The Scalar and Vector Parts . 15 1.3 The Quaternion Product . 16 1.4 The Dot Product . 16 1.5 The Cross Product . 17 1.6 Conjugates . 18 1.7 Tensor or Magnitude . 20 1.8 Versors . 20 1.9 Biradials . 22 1.10 Quaternion Identities . 23 1.11 The Biradial b/a .
    [Show full text]
  • Exploring Physics with Geometric Algebra, Book II., , C December 2016 COPYRIGHT
    peeter joot [email protected] EXPLORINGPHYSICSWITHGEOMETRICALGEBRA,BOOKII. EXPLORINGPHYSICSWITHGEOMETRICALGEBRA,BOOKII. peeter joot [email protected] December 2016 – version v.1.3 Peeter Joot [email protected]: Exploring physics with Geometric Algebra, Book II., , c December 2016 COPYRIGHT Copyright c 2016 Peeter Joot All Rights Reserved This book may be reproduced and distributed in whole or in part, without fee, subject to the following conditions: • The copyright notice above and this permission notice must be preserved complete on all complete or partial copies. • Any translation or derived work must be approved by the author in writing before distri- bution. • If you distribute this work in part, instructions for obtaining the complete version of this document must be included, and a means for obtaining a complete version provided. • Small portions may be reproduced as illustrations for reviews or quotes in other works without this permission notice if proper citation is given. Exceptions to these rules may be granted for academic purposes: Write to the author and ask. Disclaimer: I confess to violating somebody’s copyright when I copied this copyright state- ment. v DOCUMENTVERSION Version 0.6465 Sources for this notes compilation can be found in the github repository https://github.com/peeterjoot/physicsplay The last commit (Dec/5/2016), associated with this pdf was 595cc0ba1748328b765c9dea0767b85311a26b3d vii Dedicated to: Aurora and Lance, my awesome kids, and Sofia, who not only tolerates and encourages my studies, but is also awesome enough to think that math is sexy. PREFACE This is an exploratory collection of notes containing worked examples of more advanced appli- cations of Geometric Algebra (GA), also known as Clifford Algebra.
    [Show full text]
  • Multivector Differentiation and Linear Algebra 0.5Cm 17Th Santaló
    Multivector differentiation and Linear Algebra 17th Santalo´ Summer School 2016, Santander Joan Lasenby Signal Processing Group, Engineering Department, Cambridge, UK and Trinity College Cambridge [email protected], www-sigproc.eng.cam.ac.uk/ s jl 23 August 2016 1 / 78 Examples of differentiation wrt multivectors. Linear Algebra: matrices and tensors as linear functions mapping between elements of the algebra. Functional Differentiation: very briefly... Summary Overview The Multivector Derivative. 2 / 78 Linear Algebra: matrices and tensors as linear functions mapping between elements of the algebra. Functional Differentiation: very briefly... Summary Overview The Multivector Derivative. Examples of differentiation wrt multivectors. 3 / 78 Functional Differentiation: very briefly... Summary Overview The Multivector Derivative. Examples of differentiation wrt multivectors. Linear Algebra: matrices and tensors as linear functions mapping between elements of the algebra. 4 / 78 Summary Overview The Multivector Derivative. Examples of differentiation wrt multivectors. Linear Algebra: matrices and tensors as linear functions mapping between elements of the algebra. Functional Differentiation: very briefly... 5 / 78 Overview The Multivector Derivative. Examples of differentiation wrt multivectors. Linear Algebra: matrices and tensors as linear functions mapping between elements of the algebra. Functional Differentiation: very briefly... Summary 6 / 78 We now want to generalise this idea to enable us to find the derivative of F(X), in the A ‘direction’ – where X is a general mixed grade multivector (so F(X) is a general multivector valued function of X). Let us use ∗ to denote taking the scalar part, ie P ∗ Q ≡ hPQi. Then, provided A has same grades as X, it makes sense to define: F(X + tA) − F(X) A ∗ ¶XF(X) = lim t!0 t The Multivector Derivative Recall our definition of the directional derivative in the a direction F(x + ea) − F(x) a·r F(x) = lim e!0 e 7 / 78 Let us use ∗ to denote taking the scalar part, ie P ∗ Q ≡ hPQi.
    [Show full text]
  • Topological Vector Spaces and Algebras
    Joseph Muscat 2015 1 Topological Vector Spaces and Algebras [email protected] 1 June 2016 1 Topological Vector Spaces over R or C Recall that a topological vector space is a vector space with a T0 topology such that addition and the field action are continuous. When the field is F := R or C, the field action is called scalar multiplication. Examples: A N • R , such as sequences R , with pointwise convergence. p • Sequence spaces ℓ (real or complex) with topology generated by Br = (a ): p a p < r , where p> 0. { n n | n| } p p p p • LebesgueP spaces L (A) with Br = f : A F, measurable, f < r (p> 0). { → | | } R p • Products and quotients by closed subspaces are again topological vector spaces. If π : Y X are linear maps, then the vector space Y with the ini- i → i tial topology is a topological vector space, which is T0 when the πi are collectively 1-1. The set of (continuous linear) morphisms is denoted by B(X, Y ). The mor- phisms B(X, F) are called ‘functionals’. +, , Finitely- Locally Bounded First ∗ → Generated Separable countable Top. Vec. Spaces ///// Lp 0 <p< 1 ℓp[0, 1] (ℓp)N (ℓp)R p ∞ N n R 2 Locally Convex ///// L p > 1 L R , C(R ) R pointwise, ℓweak Inner Product ///// L2 ℓ2[0, 1] ///// ///// Locally Compact Rn ///// ///// ///// ///// 1. A set is balanced when λ 6 1 λA A. | | ⇒ ⊆ (a) The image and pre-image of balanced sets are balanced. ◦ (b) The closure and interior are again balanced (if A 0; since λA = (λA)◦ A◦); as are the union, intersection, sum,∈ scaling, T and prod- uct A ⊆B of balanced sets.
    [Show full text]
  • 3 Bilinear Forms & Euclidean/Hermitian Spaces
    3 Bilinear Forms & Euclidean/Hermitian Spaces Bilinear forms are a natural generalisation of linear forms and appear in many areas of mathematics. Just as linear algebra can be considered as the study of `degree one' mathematics, bilinear forms arise when we are considering `degree two' (or quadratic) mathematics. For example, an inner product is an example of a bilinear form and it is through inner products that we define the notion of length in n p 2 2 analytic geometry - recall that the length of a vector x 2 R is defined to be x1 + ... + xn and that this formula holds as a consequence of Pythagoras' Theorem. In addition, the `Hessian' matrix that is introduced in multivariable calculus can be considered as defining a bilinear form on tangent spaces and allows us to give well-defined notions of length and angle in tangent spaces to geometric objects. Through considering the properties of this bilinear form we are able to deduce geometric information - for example, the local nature of critical points of a geometric surface. In this final chapter we will give an introduction to arbitrary bilinear forms on K-vector spaces and then specialise to the case K 2 fR, Cg. By restricting our attention to thse number fields we can deduce some particularly nice classification theorems. We will also give an introduction to Euclidean spaces: these are R-vector spaces that are equipped with an inner product and for which we can `do Euclidean geometry', that is, all of the geometric Theorems of Euclid will hold true in any arbitrary Euclidean space.
    [Show full text]
  • Notes on Symmetric Bilinear Forms
    Symmetric bilinear forms Joel Kamnitzer March 14, 2011 1 Symmetric bilinear forms We will now assume that the characteristic of our field is not 2 (so 1 + 1 6= 0). 1.1 Quadratic forms Let H be a symmetric bilinear form on a vector space V . Then H gives us a function Q : V → F defined by Q(v) = H(v,v). Q is called a quadratic form. We can recover H from Q via the equation 1 H(v, w) = (Q(v + w) − Q(v) − Q(w)) 2 Quadratic forms are actually quite familiar objects. Proposition 1.1. Let V = Fn. Let Q be a quadratic form on Fn. Then Q(x1,...,xn) is a polynomial in n variables where each term has degree 2. Con- versely, every such polynomial is a quadratic form. Proof. Let Q be a quadratic form. Then x1 . Q(x1,...,xn) = [x1 · · · xn]A . x n for some symmetric matrix A. Expanding this out, we see that Q(x1,...,xn) = Aij xixj 1 Xi,j n ≤ ≤ and so it is a polynomial with each term of degree 2. Conversely, any polynomial of degree 2 can be written in this form. Example 1.2. Consider the polynomial x2 + 4xy + 3y2. This the quadratic 1 2 form coming from the bilinear form HA defined by the matrix A = . 2 3 1 We can use this knowledge to understand the graph of solutions to x2 + 2 1 0 4xy + 3y = 1. Note that HA has a diagonal matrix with respect to 0 −1 the basis (1, 0), (−2, 1).
    [Show full text]
  • Geometric-Algebra Adaptive Filters Wilder B
    1 Geometric-Algebra Adaptive Filters Wilder B. Lopes∗, Member, IEEE, Cassio G. Lopesy, Senior Member, IEEE Abstract—This paper presents a new class of adaptive filters, namely Geometric-Algebra Adaptive Filters (GAAFs). They are Faces generated by formulating the underlying minimization problem (a deterministic cost function) from the perspective of Geometric Algebra (GA), a comprehensive mathematical language well- Edges suited for the description of geometric transformations. Also, (directed lines) differently from standard adaptive-filtering theory, Geometric Calculus (the extension of GA to differential calculus) allows Fig. 1. A polyhedron (3-dimensional polytope) can be completely described for applying the same derivation techniques regardless of the by the geometric multiplication of its edges (oriented lines, vectors), which type (subalgebra) of the data, i.e., real, complex numbers, generate the faces and hypersurfaces (in the case of a general n-dimensional quaternions, etc. Relying on those characteristics (among others), polytope). a deterministic quadratic cost function is posed, from which the GAAFs are devised, providing a generalization of regular adaptive filters to subalgebras of GA. From the obtained update rule, it is shown how to recover the following least-mean squares perform calculus with hypercomplex quantities, i.e., elements (LMS) adaptive filter variants: real-entries LMS, complex LMS, that generalize complex numbers for higher dimensions [2]– and quaternions LMS. Mean-square analysis and simulations in [10]. a system identification scenario are provided, showing very good agreement for different levels of measurement noise. GA-based AFs were first introduced in [11], [12], where they were successfully employed to estimate the geometric Index Terms—Adaptive filtering, geometric algebra, quater- transformation (rotation and translation) that aligns a pair of nions.
    [Show full text]
  • Determinants in Geometric Algebra
    Determinants in Geometric Algebra Eckhard Hitzer 16 June 2003, recovered+expanded May 2020 1 Definition Let f be a linear map1, of a real linear vector space Rn into itself, an endomor- phism n 0 n f : a 2 R ! a 2 R : (1) This map is extended by outermorphism (symbol f) to act linearly on multi- vectors f(a1 ^ a2 ::: ^ ak) = f(a1) ^ f(a2) ::: ^ f(ak); k ≤ n: (2) By definition f is grade-preserving and linear, mapping multivectors to mul- tivectors. Examples are the reflections, rotations and translations described earlier. The outermorphism of a product of two linear maps fg is the product of the outermorphisms f g f[g(a1)] ^ f[g(a2)] ::: ^ f[g(ak)] = f[g(a1) ^ g(a2) ::: ^ g(ak)] = f[g(a1 ^ a2 ::: ^ ak)]; (3) with k ≤ n. The square brackets can safely be omitted. The n{grade pseudoscalars of a geometric algebra are unique up to a scalar factor. This can be used to define the determinant2 of a linear map as det(f) = f(I)I−1 = f(I) ∗ I−1; and therefore f(I) = det(f)I: (4) For an orthonormal basis fe1; e2;:::; eng the unit pseudoscalar is I = e1e2 ::: en −1 q q n(n−1)=2 with inverse I = (−1) enen−1 ::: e1 = (−1) (−1) I, where q gives the number of basis vectors, that square to −1 (the linear space is then Rp;q). According to Grassmann n-grade vectors represent oriented volume elements of dimension n. The determinant therefore shows how these volumes change under linear maps.
    [Show full text]
  • Finite Projective Geometries 243
    FINITE PROJECTÎVEGEOMETRIES* BY OSWALD VEBLEN and W. H. BUSSEY By means of such a generalized conception of geometry as is inevitably suggested by the recent and wide-spread researches in the foundations of that science, there is given in § 1 a definition of a class of tactical configurations which includes many well known configurations as well as many new ones. In § 2 there is developed a method for the construction of these configurations which is proved to furnish all configurations that satisfy the definition. In §§ 4-8 the configurations are shown to have a geometrical theory identical in most of its general theorems with ordinary projective geometry and thus to afford a treatment of finite linear group theory analogous to the ordinary theory of collineations. In § 9 reference is made to other definitions of some of the configurations included in the class defined in § 1. § 1. Synthetic definition. By a finite projective geometry is meant a set of elements which, for sugges- tiveness, are called points, subject to the following five conditions : I. The set contains a finite number ( > 2 ) of points. It contains subsets called lines, each of which contains at least three points. II. If A and B are distinct points, there is one and only one line that contains A and B. HI. If A, B, C are non-collinear points and if a line I contains a point D of the line AB and a point E of the line BC, but does not contain A, B, or C, then the line I contains a point F of the line CA (Fig.
    [Show full text]
  • New Foundations for Geometric Algebra1
    Text published in the electronic journal Clifford Analysis, Clifford Algebras and their Applications vol. 2, No. 3 (2013) pp. 193-211 New foundations for geometric algebra1 Ramon González Calvet Institut Pere Calders, Campus Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Spain E-mail : [email protected] Abstract. New foundations for geometric algebra are proposed based upon the existing isomorphisms between geometric and matrix algebras. Each geometric algebra always has a faithful real matrix representation with a periodicity of 8. On the other hand, each matrix algebra is always embedded in a geometric algebra of a convenient dimension. The geometric product is also isomorphic to the matrix product, and many vector transformations such as rotations, axial symmetries and Lorentz transformations can be written in a form isomorphic to a similarity transformation of matrices. We collect the idea Dirac applied to develop the relativistic electron equation when he took a basis of matrices for the geometric algebra instead of a basis of geometric vectors. Of course, this way of understanding the geometric algebra requires new definitions: the geometric vector space is defined as the algebraic subspace that generates the rest of the matrix algebra by addition and multiplication; isometries are simply defined as the similarity transformations of matrices as shown above, and finally the norm of any element of the geometric algebra is defined as the nth root of the determinant of its representative matrix of order n. The main idea of this proposal is an arithmetic point of view consisting of reversing the roles of matrix and geometric algebras in the sense that geometric algebra is a way of accessing, working and understanding the most fundamental conception of matrix algebra as the algebra of transformations of multiple quantities.
    [Show full text]
  • Università Degli Studi Di Trieste a Gentle Introduction to Clifford Algebra
    Università degli Studi di Trieste Dipartimento di Fisica Corso di Studi in Fisica Tesi di Laurea Triennale A Gentle Introduction to Clifford Algebra Laureando: Relatore: Daniele Ceravolo prof. Marco Budinich ANNO ACCADEMICO 2015–2016 Contents 1 Introduction 3 1.1 Brief Historical Sketch . 4 2 Heuristic Development of Clifford Algebra 9 2.1 Geometric Product . 9 2.2 Bivectors . 10 2.3 Grading and Blade . 11 2.4 Multivector Algebra . 13 2.4.1 Pseudoscalar and Hodge Duality . 14 2.4.2 Basis and Reciprocal Frames . 14 2.5 Clifford Algebra of the Plane . 15 2.5.1 Relation with Complex Numbers . 16 2.6 Clifford Algebra of Space . 17 2.6.1 Pauli algebra . 18 2.6.2 Relation with Quaternions . 19 2.7 Reflections . 19 2.7.1 Cross Product . 21 2.8 Rotations . 21 2.9 Differentiation . 23 2.9.1 Multivectorial Derivative . 24 2.9.2 Spacetime Derivative . 25 3 Spacetime Algebra 27 3.1 Spacetime Bivectors and Pseudoscalar . 28 3.2 Spacetime Frames . 28 3.3 Relative Vectors . 29 3.4 Even Subalgebra . 29 3.5 Relative Velocity . 30 3.6 Momentum and Wave Vectors . 31 3.7 Lorentz Transformations . 32 3.7.1 Addition of Velocities . 34 1 2 CONTENTS 3.7.2 The Lorentz Group . 34 3.8 Relativistic Visualization . 36 4 Electromagnetism in Clifford Algebra 39 4.1 The Vector Potential . 40 4.2 Electromagnetic Field Strength . 41 4.3 Free Fields . 44 5 Conclusions 47 5.1 Acknowledgements . 48 Chapter 1 Introduction The aim of this thesis is to show how an approach to classical and relativistic physics based on Clifford algebras can shed light on some hidden geometric meanings in our models.
    [Show full text]