In the present paper we describe Jordan matrix algebras over a field by generators and relations. We prove that the minimun number of generators of some special Jordan matrix algebras over a field is 2.
Citation: Yingyu Luo, Yu Wang, Junjie Gu, Huihui Wang. Jordan matrix algebras defined by generators and relations[J]. AIMS Mathematics, 2022, 7(2): 3047-3055. doi: 10.3934/math.2022168
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In the present paper we describe Jordan matrix algebras over a field by generators and relations. We prove that the minimun number of generators of some special Jordan matrix algebras over a field is 2.
Let F be a field of characteristic not 2. Let A be an F-algebra. By A(+) we denote the Jordan algebra induced by A in the usual manner:
a∘b=12(ab+ba). |
We call A(+) the special Jordan algebra. There exist Jordan algebras that are not special, they are called exceptional. Let S be a subset of A(+). By <S> we denote the subalgebra of A(+) generated by S. For more detailed introduction of Jordan algebras we refer the reader a book of Jacobson [7].
Let X be a nonempty set. The free algebra on X over F will be denoted by F(X). Let F(X)(+) be the Jordan algebra induced by F(X) in the usual manner. Let R be a nonempty subset of F(X)(+). By (R) we denote the ideal of F(X)(+) generated by R. This forms the Jordan factor algebra F(X)(+)/(R). By the universal property of F(X), a function f:X→A can be extended to an algebra homomorphism ˉf from F(X) into A. It is clear that ˉf induces an algebra homomorphism from F(X)(+) into A(+). Suppose that ˉf(R)=0. We note that there exists an algebra homomorphism ˆf from F(X)(+)/(R) into A(+).
Set X={ξi|i∈I} and R={fj=fj(ξi1,…,ξin(j))|j∈J}. Note that every element in R is a Jordan polynomial. For example,
2ξ1+ξ2∘ξ3−ξ43. |
Denote the coset ξi+(R) in F(X)(+)/(R) by xi. Note that
fj(xi1,…,xin(j))=0 |
for every j∈J. Following the case of algebras in [1,Section 6.2], we write F(X)(+)/(R) as L(X;R)(+). We say that this Jordan algebra is defined by the generators xi and relations fj. We always hope that the number of generators of L(X,R)(+) is the minimum. For more detailed introduction of generators and relations of algebras we refer the reader to [1,Section 6.2].
As we know, both matrix algebras and Jordan matrix algebras are important algebras that we often come across. We remand the reader to the papers [5,6,7,8,9,10,11,12,13] for a general theory of matrix Jordan algebras and the papers [2,3,4] that focus on polynomial identities of Jordan matrix algebras. It is easy to check that the minimun number of generators of matrix algebras over a field is 2 (see Proposition 1). However, it is not easy to determine the minimun number of generators of Jordan matrix algebras over a field.
In the present paper we shall describe Jordan matrix algebras over a field by generators and relations (see Theorem 2.1). We prove that the minimun number of generators of some special Jordan matrix algebras over a field is 2.
Let n≥2 be an integer. By Mn(F) we denote the algebra of all n×n matrices over F. By eij we denote the standard matrix unit of Mn(F). By δij we denote the symbol of Kronecker delta.
We begin with the following simple result.
Theorem 2.1. Let F be a field. Set
X={ξ,η,ρ}. |
Set
ξ11=ξ,ξ12=2ξ11∘η. |
We set inductively
ξ1,i+1=2ξ1i∘η |
for all i=2,…,n−1. Similarly, we set inductively
ξi+1,1=2ξi1∘ρ |
for all i=1,…,n−1. Furthemore, we set
ξij=2ξi1∘ξ1j−δijξ11 |
for all i,j=2,…,n. Let R be the following subset of L(X)(+):
ξ−ξ11;η−n−1∑i=1ξi,i+1;ρ−n−1∑i=1ξi+1,i;2ξij∘ξst−δjsξit−δitξsj,i,j,s,t=1,…,n;n∑i=1ξii−1. |
We have that L(X,R)(+)≅Mn(F)(+).
Proof. Set
x=ξ+(R);y=η+(R);z=ρ+(R);xij=ξij+(R),i,j=1,…,n. |
It follows from the elements in R that
x=x11;y=n−1∑i=1xi,i+1;z=n−1∑i=1xi+1,i;2xij∘xst=δjsxit+δitxsj,i,j,s,t=1,…,n;n∑i=1xii=1. |
It follows from the relation above that every element of L(X;R)(+) is a linear combination of the following set
T={xij|i,j=1,2,…,n}. |
We claim that T is an independent subset of L(X,R)(+). Suppose that
n∑i,j=1λijxij=0 | (2.1) |
for some λij∈F. We define a function f:X→Mn(F)(+) as follows:
f(ξ)=e11,f(η)=n−1∑i=1ei,i+1,f(ρ)=n−1∑j=1ej+1,j. |
By the universal property of F(X) we have that there exists an algebra homomorphism ˉf:F(X)(+)→Mn(F)(+) such that
ˉf(ξ)=e11,ˉf(η)=n−1∑i=1ei,i+1,ˉf(ρ)=n−1∑j=1ej+1,j |
and
ˉf(ξij)=2ˉf(ξi1∘ξ1j)−δijˉf(ξ11=2ˉf(ξi1)∘ˉf(ξ1j)−δijˉf(ξ11)=2ei1∘e1j−δije11=eij |
for all i,j=1,…,n. Note that {eij|i,j=1,…,n} is a basis of Mn(F)(+). This implies that ˉf is surjective. It is easy to check that ˉf(R)=0. Hence there exists a surjective algebra homomorphism ˆf:L(X;R)(+)→Mn(F)(+) such that
ˆf(x)=e11,ˆf(y)=n−1∑i=1ei,i+1,ˆf(z)=n−1∑j=1ej+1,j |
and
ˆf(xij)=eij |
for all i,j=1,…,n. We get from (2.1) that
n∑i=1λijeij=0. |
It implies that λij=0 for all i,j=1,…,n. Consequently, T is a basis of L(X,R)(+). In view of the above relations we get that the Jordan operation table of T is the same as that of {eij|i,j=1,…,n}, a standard basis of Mn(F)(+). Therefore L(X,R)(+)≅Mn(F)(+). The proof of the result is complete.
We remark that Theorem 2.1 implies the following result:
Corollary 1. Let F be a field. We have that
Mn(F)(+)=⟨e11,n−1∑i=1ei,i+1,n−1∑j=1ej+1,j⟩. |
In view of Corollary 2.1 we see that every Jordan matrix algebra over a field can be generated by three elements.
We remark that the minimun number of generators of matrix algebras over a field is 2. For example, we easily prove the following result. We give its proof for completeness.
Proposition 2.1. Let F be a field. We have that
Mn(F)=⟨n−1∑i=1ei,i+1,n−1∑j=1ej+1,j⟩. |
Proof. Set
E=n−1∑i=1ei,i+1,Q=n−1∑j=1ej+1,j. |
We have that
En−1Qn−1=e11∈<E,Q>. |
We get that <e11,E,Q>=<E,Q>. In view of Corollary 2.1 we note that Mn(F)(+)=<e11,E,Q>. This implies that
Mn(F)=<e11,E,Q>=<E,Q>. |
This proves the result.
We now give the main result of the paper, which shows that some special Jordan matrix algebras over a field can be generated by two elements.
Theorem 2.2. Let F be a field. Let n≥3 be an integer. Suppose that char(F)=0 or char(F)>[3(n−1)2], the integer part of 3(n−1)2. Set
X={ξ,η}. |
We set
ai=i,i=1,…,n−2;an−1=[3(n−1)2];an=n−1 |
and
(λ1λ2⋮λn)=(a1,a21,…,an1a2,a22,…,an2⋮an,a2n,…,ann)−1(10⋮0) | (2.2) |
Set
ξ11=λ1ξ∘η+λ2(ξ∘η)2+⋯+λn(ξ∘η)n. |
We set
ξ12=ξ11∘ξ. |
Furthermore, we set inductively
ξ1,i+1=[i+12]−1ξ1i∘ξ |
for all i=1,…,n−2 and
ξ1n=(n−1)−1ξ1,n−1∘ξ. |
Similarly, we set
ξ21=2ξ11∘η. |
We set inductively
ξi+1,1=2ξi1∘η |
for all i=1,…,n−1. Moreover, we set
ξij=2(ξi1∘ξ1j)−δijξ11 |
for all i,j=2,…,n. Let R be the following subset of L(X)(+):
ξ−n−2∑i=12[i+12]ξi,i+1−2(n−1)ξn−1,n;η−n−1∑i=1ξi+1,i;2ξij∘ξst−δjsξit−δitξsj,i,j,s,t=1,…,n;n∑i=1ξii−1. |
We have that L(X,R)(+)≅Mn(F)(+). Moreover, the minimun number of generators of Mn(F)(+) is 2.
Proof. Set
x=ξ+(R);y=η+(R);xij=ξij+(R),i,j=1,…,n. |
It follows from the elements in R that
x=n−2∑i=12[i+12]xi,i+1+2(n−1)xn−1,n;y=n−1∑i=1xi+1,i;2xij∘xst=δjsxit+δitxsj,i,j,s,t=1,…,n;n∑i=1xii=1. |
It follows from the relation above that every element of L(X;R)(+) is a linear combination of the following set
T={xij|i,j=1,2,…,n}. |
We claim that T is an independent subset of L(X,R)(+). Suppose that
n∑i,j=1λijxij=0 | (2.3) |
for some λij∈F. We define a function f:X→Mn(F)(+) as follows:
f(ξ)=2(n−2∑i=1[i+12]ei,i+1+(n−1)en−1,n),f(η)=n−1∑j=1ej+1,j. |
By the universal property of F(X) we have that there exists an algebra homomorphism ˉf:F(X)(+)→Mn(F)(+) such that
ˉf(ξ)=2(n−2∑i=1[i+12]ei,i+1+(n−1)en−1,n),ˉf(η)=n−1∑j=1ej+1,j |
and
ˉf(ξ∘η)=ˉf(ξ)∘ˉf(η)=2(n−2∑i=1[i+12]ei,i+1+(n−1)en−1,n)∘(n−1∑j=1ej+1,j)=n−1∑i=1ieii+[3(n−1)2]en−1,n−1+(n−1)enn=n∑i=1aieii. |
We get from (2.2) that
ˉf(ξ11)=ˉf(λ1ξ∘η+λ2(ξ∘η)2+⋯+λn(ξ∘η)n)=λ1ˉf(ξ∘η)+λ2ˉf(ξ∘η)2+⋯+λnˉf(ξ∘η)n=λ1(n∑i=1aieii)+λ2(n∑i=1aieii)2 +⋯+λn(n∑i=1aieii)n=(λ1a1+λ2a21+⋯+λnan1)e11+⋯+ (λ1an+λ2a2n+⋯+λnann)enn=e11. |
We have that
ˉf(ξ12)=ˉf(ξ11∘ξ)=ˉf(ξ11)∘ˉf(ξ)=e11∘(n−2∑i=12[i+12]ei,i+1+2(n−1)en−1,n)=e12 |
and
ˉf(ξ1,i+1)=[i+12]−1ˉf(ξ1i∘ξ)=e1,i+1 |
for all i=1,…,n−2. Moreover, we have that
ˉf(ξ1n)=(n−1)−1ˉf(ξ1,n−1∘ξ)=e1n. |
Similarly, we have that
ˉf(ξi1)=ei1 |
for all i=2,…,n−1. Moreover, we have that
ˉf(ξij)=2ˉf(ξi1∘ξ1j)−δijˉf(ξ11)=2ei1∘e1j−δije11=eij |
for all i,j=2,…,n. Note that {eij|i,j=1,…,n} is a basis of Mn(F)(+). This implies that ˉf is surjective. It is easy to check that ˉf(R)=0. Hence there exists a surjective algebra homomorphism ˆf:L(X;R)(+)→Mn(F)(+) such that
ˆf(x)=n−2∑i=12[i+12]ei,i+1+2(n−1)en−1,n,ˆf(y)=n−1∑j=1ej+1,j. |
Moreover, we have that
ˆf(x1j)=e1j,ˆf(xi1)=ei1 |
for all i,j=1,…,n and so
ˆf(xij)=eij |
for all i,j=1,…,n. It follows from (2.3) that
n∑i,j=1λijeij=0. |
This implies that λij=0 for all i,j=1,…,n. Consequently, T is a basis of L(X,R)(+). In view of the above relations we see that the Jordan operation table of T is the same as that of {eij|i,j=1,2,…,n}, a standard basis of Mn(F)(+). Therefore L(X,R)(+)≅Mn(F)(+).
Suppose that Mn(F)(+)=<A> for some A∈Mn(F)(+). It is clear that Mn(F)=<A>. This implies that Mn(F) is commutative, a contradiction. We get that the minimun number of generators of Mn(F)(+) is 2. The proof of the result is complete.
We remark that Theorem 2.2 implies the following result:
Corollary 2.2. Let F be a field. Let n≥3 be an integer. Suppose that char(F)=0 or char(F)>[3(n−1)2]. We have that
Mn(F)(+)=⟨n−2∑i=12[i+12]ei,i+1+2(n−1)en−1,n,n−1∑j=1ej+1,j⟩. |
The main conclusion of the paper is to show that the minimun number of generators of Mn(F)(+) (where n≥3 and char(F)=0 or char(F)>[3(n−1)2]) is 2.
The authors are grateful to the referees for useful comments.
The authors declare no conflicts of interest in this paper.
[1] | M. Brešar, Introduction to nocommutative algebras, Springer, 2014. doi: 10.1007/978-3-319-08693-4. |
[2] |
L. Centrone, F. Martino, A note on cocharacter sequence of Jordan upper triangular matrix algebra, Commun. Algebra, 45 (2017), 1687–1695. doi: 10.1080/00927872.2016.1222408. doi: 10.1080/00927872.2016.1222408
![]() |
[3] |
L. Centrone, F. Martino, M. da Silva Souza, Specht property for some varieties of Jordan algebras of almost polynomial growth, J. Algebra, 521 (2019), 137–165. doi: 10.1016/j.jalgebra.2018.11.017. doi: 10.1016/j.jalgebra.2018.11.017
![]() |
[4] |
A. Cirrito, F. Martino, Ordinary and graded cocharacter of the Jordan algebra of 2×2 upper triangular matrices, Linear Algebra Appl., 451 (2004), 246–259. doi: 10.1016/j.laa.2014.03.011. doi: 10.1016/j.laa.2014.03.011
![]() |
[5] |
C. Costara, Nonlinear invertibility preserving maps on matrix algebras, Linear Algebra Appl., 602 (2020), 216–222. doi: 10.1016/j.laa.2020.05.010. doi: 10.1016/j.laa.2020.05.010
![]() |
[6] |
M. Grašič, Zero product determined Jordan algebra, Linear Multilinear Algebra, 59 (2011), 671–685. doi: 10.1080/03081087.2010.485199. doi: 10.1080/03081087.2010.485199
![]() |
[7] | N. Jacobson, Structure and representations of Jordan algebras, Colloquium Publications, Vol. 39, American Mathematical Society, 1968. |
[8] |
M. Kochetov, F. Y. Yasumura, Group grading on the Lie and Jordan algebras of block-triangular matrices, J. Algebra, 537 (2019), 147–172. doi: 10.1016/j.jalgebra.2019.07.020. doi: 10.1016/j.jalgebra.2019.07.020
![]() |
[9] |
X. B. Ma, G. H. Ding, L. Wang, Square-zero determined matrix algebras, Linear Multilinear Algebra, 59 (2011), 1311–1317. doi: 10.1080/03081087.2010.539606. doi: 10.1080/03081087.2010.539606
![]() |
[10] | K. McCrimmon, A taste of Jordan algebras, Springer, 2004. doi: 10.1007/b97489. |
[11] |
H. P. Pertersson, The isotopy problem for Jordan matrix algebras, Trans. Amer. Math. Soc., 244 (1978), 185–197. doi: 10.1090/S0002-9947-1978-0506615-7. doi: 10.1090/S0002-9947-1978-0506615-7
![]() |
[12] |
C. C. Xi, J. B. Zhang, Structure of centralizer matrix algebras, Linear Algebra Appl., 622 (2021), 215–249. doi: 10.1016/j.laa.2021.03.034. doi: 10.1016/j.laa.2021.03.034
![]() |
[13] |
D. Y. Wang, Q. Hu C. G. Xia, Jordan derivation of certain Jordan matrix algebras, Linear Multilinear Algebra, 56 (2008), 581–588. doi: 10.1080/03081080701492165. doi: 10.1080/03081080701492165
![]() |