Split Quaternion Matrices
Total Page:16
File Type:pdf, Size:1020Kb
View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Repository of the Academy's Library Miskolc Mathematical Notes HU e-ISSN 1787-2413 Vol. 13 (2012), No 2, pp. 223-232 DOI: 10.18514/MMN.2012.364 Split quaternion matrices Yasemin Alagöz, Kür³at Hakan Oral, and Salim Yüce Miskolc Mathematical Notes HU e-ISSN 1787-2413 Vol. 13 (2012), No. 2, pp. 223–232 SPLIT QUATERNION MATRICES YASEMIN ALAGOZ,¨ KURS¸AT¨ HAKAN ORAL, AND SALIM YUCE¨ Received 7 June, 2011 Abstract. In this paper, we consider split quaternions and split quaternion matrices. Firstly, we give some properties of split quaternions. After that we investigate split quaternion matrices using properties of complex matrices. Then we define the complex adjoint matrix of split qua- ternion matrices and we describe some of their properties. Furthermore, we give the definition of q-determinant of split quaternion matrices. 2000 Mathematics Subject Classification: 11R52; 15A33 Keywords: quaternions, split quaternions, matrices of split quaternions 1. INTRODUCTION Sir William Rowan Hamilton introduced the set of quaternions in 1843, which can be represented as H a a0 a1i a2j a3k a0;a1;a2;a3 R Df D C C C W 2 g where i 2 j 2 k2 1 and ijk 1. One can see easily that ij j i k. Thus the setD of quaternionsD D is a skew-field.D Since quaternions are non-commutative,D D they differs from complex numbers .C/ and real numbers .R/. For example, for matrices of quaternions the left eigenvalues and the right eigenvalues must be not the same. Because of this, various authors have been studied quaternion matrices, for example [1], [4], [5] and [6]. After the work of Hamilton, in 1849, James Cockle introduced the set of split quaternions, which can be represented as Hs q q0 q1i q2j q3k q0;q1;q2;q3 R Df D C C C W 2 g where i 2 1; j 2 k2 1 and ijk 1. This set is 4-dimensional like the set D D D D of quaternions. Hs is noncommutative, too. But Hs contains zero-divisors, nilpotent elements and nontrivial idempotents. For more properties of split quatenions the reader is referred to [2] and [3]. In this paper, we will investigate split quaternion matrices. Firstly in Section 2, we will give some properties of split quaternions which will be used in the following sections. After that, in Section 3, we will introduce split quaternion matrices and give some properties of them. Finally in Section 4, we define the complex adjoint matrix c 2012 Miskolc University Press 224 YASEMIN ALAGOZ,¨ KURS¸AT¨ HAKAN ORAL, AND SALIM YUCE¨ of split quaternion matrices and we give some properties of these matrices. Then we will define the determinant of a split quaternion matrices using its adjoint matrix. 2. SPLIT QUATERNIONS A split quaternion q is a vector of the form q a0 a1i a2j a3k D C C C where a0;a1;a2;a3 are real numbers. Split quaternion algebra is an associative, non-commutative, non-division ring with four basis elements 1;i;j;k satisfying the equalities f g i 2 1; j 2 k2 1; D D D ij j i k; jk kj i; ki ik j . D D D D D D Let us denote the algebra of split quaternions by HS . For any q a0 a1i a2j D C C C a3k HS we define Req a0, the real part of q; Imq a1i a2j a3k, the 2 D D C C imaginary part of q. The conjugate of a split quaternion is denoted by q q and it is DN q q a0 a1i a2j a3k. D D The norm of a split quaternion is defined as p qˇ ˇ q qq ˇIqˇ k k D j j D 2 2 2 2 where Iq qq a0 a1 a2 a3.If q 1 then q is called unit split quaternion. D qD C k k D Note that p is a unit split quaternion for q HS with q 0. The inverse of D q 2 k k ¤ the split quaternionk k q is 1 q q , if Iq 0. D Iq ¤ Theorem 1. Split quaternions satisfy the following properties for the elements p;q and r HS . .i/ q q qq2 , D .ii/ jc cj or jcj c for any complex number c, D 2 D 2 .iii/ q2 Req Imq 2Req Imq, D j j k k C .iv/ .qp/ pq, .v/ .pq/r Dp .qr/, .vi/ pq Dqp in general, .vii/ q ¤ q if and only if q is a real number, D .viii/ q is the inverse of q if a2 a2 a2 a2, Iq 0 C 1 ¤ 2 C 3 .ix/ Every split quaternion q can be uniquely expressed as q c1 c2j; where c1 D C and c2 are complex numbers. Theorem 2. Every split quaternion can be represented by a 2 2 complex matrix. SPLIT QUATERNION MATRICES 225 Proof. Let q HS , then there exist complex numbers a1 and a2 such that q a1 2 D C a2j by Theorem 1.ix/. The linear map fq HS HS is defined by fq .p/ pq W ! D for all p HS . This map is bijective and 2 fq .1/ 1.a1 a2j / a1 a2j D C D C fq .j / j .a1 a2j / a2 a1j . D C D C With this transformation split quaternions are defined as subset of the matrix ring M2 .C/, the set of 2 2 complex matrices:  a a à 0 1 2 HS a1;a2 C . D a2 a1 I 2 0 HS and HS are essentially the same. Note that,  a a à 0 1 2 0 M q a1 a2j HS q HS W D C 2 ! D a2 a1 2 2 is bijective and preserves the operations. Furthermore q detq0 . k k D 3. SPLIT QUATERNION MATRICES The set Mm n .HS / denotes all m n type matrices with split quaternion entries. If m n, then the set of split quaternion matrices is denoted by Mn .HS /. The ordin- D ary matrix addition and multiplication are defined. With these operations Mn .HS / is a ring with a unit. The left (right) scalar multiplication is defined as, for A .ast / D 2 Mm n .HS /, q HS , 2 qA .qast / and Aq .ast q/: D D Here for B Mn o .HS /; p HS we obtain 2 2 q .AB/ .qA/B; D .Aq/B A.qB/; D .pq/A p .qA/: D Mm n .HS / is a left (right) vector space over HS : For A .ast / Mm n .HS /, A .ast / ast Mm n .HS / is the conjugate D 2 D D 2 T T of A; A .ats/ Mn m .HS / is the transpose of A; A A Mn m .HS / is the conjugateD transpose2 of A. D 2 For a square matrix A Mn .HS / if AA AA then A is called a normal matrix; if A A then A is called2 a Hermitian matrix;D if AA I then A is called a unitary D D matrix; for B Mn .HS / if AB BA I then A is an invertible matrix. 2 D D 226 YASEMIN ALAGOZ,¨ KURS¸AT¨ HAKAN ORAL, AND SALIM YUCE¨  i j à  i k à Example 1. Let A , B M2 .HS /. Then, D 0 k D 0 j 2  i 1 à  i j à .i/ A 1 and A D 0 k D 0 k  à  à 1 i 1 i 1 .ii/ A A 1 D 0 k ¤ 0 k D  à  à T 1 i 0 i 0 1T .iii/ A A D 1 k ¤ 1 k D  1 j 1 à  1 j 1 à .iv/ AB C C A B D 0 i ¤ 0 i D  à  à T 1 0 1 0 .v/ .AB/ BT AT D j 1 i ¤ j 1 i D C C With these examples we get the following Corollary for split quaternion matrices. Corollary 1. Let A Mm n .HS / and B Mn o .HS /. Then the followings are satisfied: 2 2 1 .i/ A A 1 in general; ¤ T 1 1T .ii/ A A in general; ¤ .iii/ AB A B in general; ¤ .iv/ .AB/T BT AT in general. ¤ Theorem 3. Let A Mm n .HS / and B Mn o .HS /. Then, T 2 2 .i/ A AT , D .ii/ .AB/ BA, D1 1 1 .iii/ .AB/ B A if A and B are invertible, 1 D 1 .iv/ .A / A if A is invertible. D Proof. .i/,.iii/ and .iv/ can be easily shown. Now we will prove .ii/. .ii/ Let A A1 A2j and B B1 B2j , where A1;A2;B1 and B2 are complex matrices. ThenD C D C .AB/ A1B1 A2B2 A1B2 A2B1 j D C C C T A1B1 A2B2 A1B2 A2B1 j D C C T T A1B1 A2B2 A1B2 A2B1 j D C C T T T T T T T T B1 A1 .B2/ A2 .B2/ .A1/ j B1 .A2/ j . D C On the other hand, for T T T T B B1 .B2/ j and A A1 .A2/ j D D SPLIT QUATERNION MATRICES 227 we can obtain T T Á T T Á B A B1 .B2/ j A1 .A2/ j D T T T T T T T T B1 A1 .B2/ A2 .B2/ .A1/ j B1 .A2/ j .