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J. Math. Comput. Sci. 10 (2020), No. 1, 1-26 https://doi.org/10.28919/jmcs/4247

ISSN: 1927-5307

MINIMAL CYCLIC CODES OF LENGTH 16pn OVER GF(q), WHERE qIS PRIME OR PRIME POWER OF THE FORM 16k+7

VISHVAJIT SINGH1,∗, MANJU PRUTHI1, JAGBIR SINGH2

1Department of Mathematics, I.G. University, Meerpur, Rewari, India 2Department of Mathematics, Maharshi Dayanand University, Rohtak, India

Copyright c2020 the author(s). This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract. In this paper, the expressions for primitive idempotents in group algebra of cyclic group G of length 16pn, wherepis prime andqis some prime or prime power (of type 16k+7),nis a positive integer, order ofq

modulopnis φ(pn)

2 , are obtained. Associated with this the generating polynomials and minimum distance bounds

for the corresponding cyclic codes are obtained.

Keywords:cyclotomic cosets; primitive idempotents; generating polynomials; minimum distance.

2010 AMS Subject Classification:1T71, 11T55, 22D20.

1.

INTRODUCTION

The group algebra FC16pn, F is field of order q and C16pn is cyclic group of order 16pn

such thatg.c.d.(q,16p) =1, is semi-simple having finite cardinality of collection of primitive

idempotents which is equal to the cardinality of collection ofq-cyclotomic cosets modulo 16pn.

The primitive idempotents of minimal cyclic codes of lengthm, where order ofqmodulomis

φ(m) for m=2,4,pn,2pn were calculated by Pruthy and Arrora. The primitive idempotents

of length pn with order ofq modulo pn is φ(p2n) were computed by Arora et. all and minimal ∗Corresponding author

E-mail address: vishvajit73.sheoran@gmail.com Received August 4, 2019

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quadratic residue codes of length pn by Batra and Arrora. Cyclic codes of length 2pn over

F, where order ofqmodulo 2pnis φ(2p2n) were calculated by Batra and Arrora. Minimal cyclic codes of lengthpnq, wherepandqare distinct odd primes were computed by Sahni and Bakshi.

Further, when order of q modulo pn is φ(pn), the minimal cyclic codes of length 8pn were

obtained by J. Singh and Arrora. Irreducible cyclic codes of length 4pn and 8pn, where q≡

3(mod8)andp/(q−1)were obtained in [2].

In this paper, we computed cyclic codes of length 16pnoverF whereqis some prime or prime

power of the form 16k+7 and order of q modulo pn is φ(p2n). For every odd prime p, there exist an integer gsuch that 1<g<16p which is primitive root modulo p. For p of the type

4k+1, the order ofgmodulo 4, modulo 8 is 2 and modulo 16 is 4 and for pof the form 4k+3

then order of g modulo 4, modulo 8 and modulo 16 is 2. Forqany prime or prime power with

(q,p) =1, there existg∈ {1,/ q,q2, ...,qφ(2p)−1}. ForS={1,2, ...,16pn}and for alla,b∈S, the

equivalence relation defined by a≡bqi(mod 16pn) for some integer i≥0, partition the setS

into 32n+9 equivalent classes namelyq− cyclotomic cosets modulo 16pn given by Ωapn =

{apn}fora∈ {0,8},

bpn ={bpn,bpnq}forb∈B={1,2,3,4,6,9,11}and for 0≤i≤n−1,

t pi={t pi,t piq, ...,t piq

φ(pn−i)

2 −1},

tgpi={tgpi,tgpiq,tgpiq2, ...,tgpiq

φ(pn−i)

2 −1}, such thatt∈

A={1,2,4,8,16,λ,2λ,4λ,µ,2µ,ν,2ν,η,ξ,ρ,χ},A0=BS{0,8}. We are taking the case for

pis a prime of the form 8k+1. However in the other cases whenever p is prime or prime power

of the type 8k+3, 8k+5 and 8k+7 the expression for primitive idempotents can be computed

by using permutation on the setA. Idempotents corresponding toΩt pnfort∈Bare computed in

the section 2. In section 3, we compute expression for primitive idempotents corresponding to

t pi fott =8,16,8g,16gand fort =2,4,2λ,4λ,2µ,2ν,2g,4g,2λg,4λg,2µg,2νgin section

4. And rest of all expressions are obtained in section 5. In section 6, we derived the generating

polynomials and dimensions for the corresponding cyclic codes of length 16pn. Section 7

consist of minimum distance or the bounds for minimum distance of these codes. At the end,

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2.

PRIMITIVE IDEMPOTENTSCORRESPONDING TOΩt pn,t ∈A0

Throughout this paper, we considerα to be 16pnth root of unity in some extension field ofF.

LetMsbe the minimal ideal inR16pn= F[x]

<x16pn1>∼=FC16pn, generated by

(x16pn−1)

ms(x) , wherems(x)

is the minimal polynomial for αs, s∈Ωs. We take Ps(x), the primitive idempotent in R16pn,

corresponding to the minimal idealMs, given byPs(x) = 161pn 16pn−1

t=0

εisxs whereεis =

s∈Ωs

α−is

andCs=

s∈Ωs

xs.

Then,

(1) Ps(x) = 1

16pn[

a∈A0

εaps nCapn+ n−1

i=0

{

a∈A

εaps iCapi+

a∈A

εagps iCagpi}]

Lemma 2.1. For cyclotomic cosets Ωapn, a ∈ A0, apn = −Ω(8+a)pn if a ∈ {1,3} and

Ωapn =−Ωapn if a∈ {2,4,6,8}.

Proof. Since Ωapn ={apn}, so {(8+a)pnq+apn}= pn{(8+a)q+a}= pn{(8+a)(16k+

7) +a} ≡0(mod16pn). Similarly other result holds.

Theorem 2.2. The explicit expression for the primitive idempotents Papn, a,w∈A0in R16pn are

given by

Pwpn(x) = 1

16pn[{

a∈A0

(−1)waαwap

2n

Cpn} +

n−1

i=0

{

a∈A

(−1)waαwap

n+i

Capi +

a∈A

(−1)waαwagp

n+i

Cagpi}].

Proof. By definition,εis=

sεΩs

α−isand Cs=

sεΩs

xswhereα is16pnth root of unity. For s=0,

since εk0 =1 for every 0≤ k≤ 16pn−1, therefore P0(x) = 161pn[

a∈A0

Capn+ n−1

i=0

{

a∈A

Capi+

a∈A

Cagpi}].

From lemma2.1,Ωpn =−Ω9pn, thereforeεp n k =

sεΩpn

α−ks=α−p

nk

=α9p

nk

εp

n 0 =−ε

pn

8pn =1, εp n

pn =−εp n

9pn =−αp

2n

, εp

n

2pn =α2p

2n

,

εp

n

3pn =−ε pn

11pn =−α3p

2n

, εp

n

4pn =α4p

2n

, εp

n

6pn =α6p

2n

,

εp

n pi =−ε

pn

ηpi=−αp n+i

, εp

n 2pi =−ε

pn

2µpi=α2pn+i, ε pn 4pi =−ε

pn

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εp

n 8pi =−ε

pn

16pi=−1, ε pn

λpi =−ε pn

ξpi=−αλp n+i

, εp

n

2λpi =−ε pn

2νpi =α2λp n+i

,

εp

n

µpi=−ε pn

ρpi =−αµp n+i

, εp

n

νpi=−ε pn

χpi =−ανp n+i

, εp

n gpi=−ε

pn

ηgpi=−αgp n+i

,

εp

n

2gpi=−ε pn

2µgpi=α2gp n+i

, εp

n

4gpi=−ε pn

4λgpi =α4gp n+i

, εp

n

8gpi=−ε pn

16gpi=−1,

εp

n

λgpi =−ε pn

ξgpi =−αλgp n+i

, εp

n

2λgpi =−ε pn

2νgpi=α2λgp n+i

, εp

n

µgpi=−ε pn

ρgpi=−αµgp n+i

,

εp

n

νgpi =−ε pn

χgpi=−ανgp n+i

, .

Using all these in(2.1)the expression for Ppn(x)can be computed.

Similarly, by lemma2.1, Pwpn(x), w∈A0− {0,1}can be computed.

3.

PRIMITIVE IDEMPOTENTSCORRESPONDING TOPt pi,t=8,16,8g,16g

We defineHj=pj

sεΩ8gp j

αs;Ij=pj

sεΩ16gp j

αs ;Qj=pj

sεΩ8p j

αs ;Rj= pj

sεΩ16p j

αs, for 0≤

j≤n−1. SinceQqj = (pj

sεΩ8p j

αs)q= (pj)q(

sεΩ8p j

αs)q= (pj)q

sεΩ8p j

αqs= (pj)q

sεqΩ8p j αs.

However, (pj)q = pj, so Qqj = pj

sεqΩ8p j

αs. Moreover, Ω8pj is a cyclotomic coset, so

qΩ8pj=Ω8pj. HenceQqj =pj

sεΩ8p j

αs=Qj andQj∈GF(q). SimilarlyHj,Ij,Rj∈GF(q).

Lemma 3.1. Ij+Rj=

−pn−1if j=n1

0otherwise.

for0≤ j≤n−1.

Proof. By definition Ij+Rj=pj φ(pn−j)

2 −1

t=0

(δgqt+δq

t

)whereδ =α16pj.

The set{1,q,q2, ...,qφ(pn −j)

2 −1,g,gq,gq2, ...,gq

φ(pn−j)

2 −1}is a reduced residue system mod(pn−j)

so Ij+Rj= pj[

pn−j

t=0

δt−

pn−j

t=1,p/t

δt] =pj[

pn−j

t=0

δt−

pn−j−1

t=1

δpt] = 

−pn−1if j=n1

0otherwise.

Lemma 3.2. For0≤ j≤n−1, Hj+Qj=

pn−1if j=n−1 0otherwise.

Proof. This result can be computed on similar lines as that of lemma 3.1 and using that {1,q,q2, ...,qφ(pn

−j)

2 −1,g,gq,gq2, ...,gq

φ(pn−j)

2 −1}is a reduced residue system mod(2pn−j).

Lemma 3.3. For cyclotomic cosetsΩpi,0≤i≤n−1

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(ii)µ2Ωpi=Ωηpi=ηΩpi=ρ2Ωpi =λ2Ωpi=ξ2Ωpi

(iii) (2λ)2Ωpi =2Ω2pi=4Ωpi=Ω4pi= (2µ)2Ωpi= (2ν)2Ωpi

(iv) (4λ)2Ωpi =Ω16pi=2Ω8pi=4Ω4pi=16Ωpi.

Proof. (i) Since η = 1+8pn. Therefore η2 = (1 +8pn)2 = 1+64p2n +16pn ≡ 1(mod16pn). This implies η2 ≡ 1(mod16pn) ⇒ η2Ωpi = Ωpi. Now η2Ωpi =

{η2pi,η2piq,η2piq2, ...,η2piqφ(pn −i)

2 −1}=η{ηpi,ηpiq,ηpiq2, ...,ηpiq

φ(pn−i)

2 −1}

=ηΩηpi. Now ν2= (1+6pn)2=1+36p2n+12pn≡1(mod16pn)and χ2= (1+14pn)2=

1+196p2n+28pn=1(mod16pn). Henceν2Ωpi =χ2Ωpi =Ωpi. Similarly other result holds.

Lemma 3.4. (i)Ω(1+t pn)pi =−Ω{1+(14t)pn}pi and henceΩ(1+t pn)gpi =−Ω{1+(14t)pn}gpi, for

t=0,2,4,6

(ii)Ω2(1+t pn)pi =−Ω2{1+(6t)pn}pi and henceΩ2(1+t pn)gpi =−Ω2{1+(6t)pn}gpi, for t=0,2

(iii)Ω4pi=−Ω4λpi and henceΩ4gpi=−Ω4λgpi,

(iv)Ωt pi =−Ωt pi and henceΩtgpi =−Ωtgpi, for t=8,16. Where1≤i≤n−1.

Proof. Sinceχ=1+14pn≡ −1(mod16)and q

φ(pn)

2 ≡1(mod16). Further, q

φ(pn)

4 ≡1(mod16),

as q ≡ 1(mod16), therefore χq

φ(pn)

4 ≡ −1(mod16). Also q

φ(pn)

2 ≡ 1(mod pn) so q

φ(pn)

4 ≡

−1(mod pn) and χ ≡ 1(mod pn), thus χq

φ(pn)

4 ≡ −1(mod pn). However (16,pn) = 1 thus

χq

φ(pn)

4 ≡ −1(mod16pn)and so−Ω

χpi=Ωpi. Hence−Ωχgpi =Ωgpi.

Proof of remaining parts can be computed using relations of congruences and similar reasons

as for the relation obtained.

Lemma 3.5. For0≤i≤n; 0≤ j≤n−1,

sεΩp j α8gp

is

=

sεΩ2p j α4gp

is

=

sεΩ2p j α4λgp

is

=

sεΩ4p j α2λgp

is

=

sεΩ4p j α2µgp

is

=

sεΩ4p j α2νgp

is

=

sεΩ8p j αλgp

is

=

sεΩ8p j αµgp

is

=

sεΩ8p j ανgp

is

=

sεΩ8p j αηgp

is

=

sεΩ8p j αξgp

is

=

sεΩ8p j αρgp

is

=

sεΩ8p j αχgp

is

=

sεΩ2

λp j

α4λgp

is

=

sεΩ4

λp j

α2µgp

is

=

sεΩ4

λp j

α2νgp

is

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        

−φ(pn−j)

2 , i f i+j≥n, 1

pjHi+j, i f i+ j≤n−1, g6=1, 1

pjQi+j, i f i+j≤n−1, g=1.

Proof. Asα is16pnth root of unity in some extension field of GF(q), so

sεΩ4

λp j

α2νgp

is

=

φ(pn−j)

2 −1

t=0

α8(1+2p

n)(1+6pn)gpi+jqt

=

φ(pn−j)

2 −1

t=0

α8gp

i+jqt

=

sεΩp j α8gp

is

.

Ifβ =α8gpi

+j

then

sεΩp j α8gp

is

=

φ(pn−j)

2 −1

t=0

(α8gpi+jqt) =

φ(pn−j)

2 −1

t=0

(βqt).

For i+j≥n,βis16th root of unity, and therefore

sεΩp j α8gp

is

=

φ(pn−j)

2 −1

t=0

α8gp

i+jqt

=−φ(p

n−j)

2 .

If i+ j≤n−1, β is 16pn−i−jth root of unity. Then βql =βqr which is possible when l≡

r(modφ(pn2−i−j)). So

sεΩp j α8gp

is

= φ(p

n−j)

φ(pn−i−j)

φ(pn−i−j)

2 −1

t=0 βq t = p i+j

pj

sεΩ8gpi+j

αs= 1

pjHi+j.

Similar result hold for Qi+j.

Proof of lemma 3.6, similarly can be obtained using definition ofIjandRj.

Lemma 3.6. For0≤i≤n;0≤ j≤n−1

sεΩp j α16gp

is

=

sεΩ2p j α8gp

is

=

sεΩ2p j α16gp

is

=

sεΩ4p j α4gp

is

=

sεΩ4p j α8gp

is

=

sεΩ4p j α16gp

is

=

sεΩ4p j α4λgp

is

=

sεΩ8p j α16gp

is

=

sεΩ8p j α2λgp

is

=

sεΩ8p j α4λgp

is

=

sεΩ8p j α2µgp

is

=

sεΩ8p j α2νgp

is

=

sεΩ16p j α16gp

is

=

sεΩ16p j αλgp

is

=

sεΩ16p j α2λgp

is

=

sεΩ16p j α4λgp

is

=

sεΩ16p j αµgp

is

=

sεΩ16p j α2µgp

is

=

sεΩ16p j ανgp

is

=

sεΩ16p j α2νgp

is

=

sεΩ16p j αηgp

is

=

sεΩ16p j αξgp

is

=

sεΩ16p j αρgp

is

=

sεΩ16p j αχgp

is

=

sεΩ4

λp j

α4λgp

is =         

φ(pn−j)

2 ,i f i+j≥n, 1

pjIi+j, i f i+ j≤n−1, g6=1, 1

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Theorem 3.7. When p≡1(mod8), the expressions for primitive idempotents corresponding to P8pi, P8gpi, P16pi and P16gpiin R16pn are given by

P8pj(x) = 161pn[

φ(pn−j) 2 {

t∈A0

(−1)tCt pn} + φ(p

n−j) 2

n−1

i=n−j

{

a∈A

(−1)a{Capi + Cagpi}} +

1 pj

n−j−1

i=0

{Qi+j(Cpi+Cλpi+Cµpi+Cνpi+Cηpi+Cξpi +Cρpi+Cχpi) +Ri+j(C2pi +C4pi+

C8pi+C16pi+C2λpi+C4λpi+C2µpi+C2νpi) +Hi+j(Cgpi+Cλgpi+Cµgpi+Cνgpi+Cηgpi+

Cξgpi +C

ρgpi +Cχgpi) +Ii+j(C2gpi +C4gpi +C8gpi +C16gpi +C2λgpi +C4λgpi +C2µgpi +

C2νgpi)}]

P16pj(x) = 161pn[

φ(pn−j)

2 {

t∈A0

Ct pn} + φ(p n−j) 2

n−1

i=n−j

{

a∈A

{Capi + Cagpi}} +

1 pj

n−j−1

i=0

{

a∈A

{Ri+jCapi+Ii+jCagpi}}]

where Qn1 = 12[pn−1+

pn−1(16pn+7p7)

4 ], Hn−1 = 1 2[p

n−1

pn−1(16pn+7p7)

4 ], In−1 = 1

2[−pn−1+

pn−1(16pn+7p7)

4 ]and Rn−1=− 1

2[pn−1+

pn−1(16pn+7p7)

4 ]and for every j≤n−2

Qj=Hj=Ij=Rj=0.

Proof. SinceΩ8pj =−Ω8pj, as obtained in lemma3.4, soε8p j k =

sεΩp j

α−ks=

sεΩp j α8ks.

Thusε8p

j

t pn = (−1)tφ (pn−j)

2 for t ∈A

0 and using Lemma 3.3, 3.53.6, wherever is required we

obtain

ε8p

j pi =ε

8pj

λpi =ε 8pj

µpi =ε 8pj

νpi =ε 8pj

ηpi =ε 8pj

ξpi =ε 8pj

ρpi =ε 8pj

χpi =

−φ(pn−j)

2 if i+ j≥n 1

pjQi+jif i+j≤n−1

ε8p

j 2pi =ε

8pj 4pi =ε

8pj 8pi =ε

8pj 16pi=ε

8pj 2λpi=ε

8pj 4λpi =ε

8pj 2µpi=ε

8pj 2νpi=

φ(pn−j)

2 if i+j≥n 1

pjRi+jif i+j≤n−1

ε8p

j gpi =ε

8pj

λgpi =ε 8pj

µgpi =ε 8pj

νgpi=ε 8pj

ηgpi=ε 8pj

ξgpi=ε 8pj

ρgpi=ε 8pj

χgpi =

−φ(p2n−j) if i+j≥n

1

pjHi+jif i+j≤n−1

ε8p

j 2gpi=ε

8pj 4gpi =ε

8pj 8gpi=ε

8pj 16gpi=ε

8pj 2λgpi =ε

8pj 4λgpi=ε

8pj 2µgpi =ε

8pj 2νgpi=

φ(pn−j)

2 if i+j≥n 1

pjIi+jif i+j≤n−1

Using all these in(2.1), expression for P8pj is obtained.

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the expression for P8gpj(x), P16gpj(x) can be written by interchanging Q and R by H and I in

the expressions of P8pj, P16pj.

Since Ck=

sεΩk

xs and (Ck)

α16p j =Ck(α

16pj) =

sεΩk

(α16pj)s. Therefore Ct pn(α16p j

) =1 for

t∈A0.

Capi(α16p j

) = 

φ(pn−j)

2 ,i f i+j≥n 1

pjRi+j,i f i+j≤n−1.

and Cagpi(α16p j

) = 

φ(pn−j)

2 ,i f i+j≥n 1

pjIi+j,i f i+j≤n−1.

Using all these in P16pj(α16p j

) =1, to obtain

16pn=φ(p2n−j)[9+

n−1

i=n−j

φ(pn−j)

2 32] + 1 pj

n−j−1

i=0

1 pi(16R

2

i+j+16I2i+j)

which in turn implies 1

pj n−j−1

i=0

1 pi(R

2

i+j+I2i+j) =

pn−1

2 (p+1) +

7pn−j−1

32 (p−1).

In particular for j=n−1, 1

pn−1(R

2

n−1+I2n−1) = p n−1

2 (p+1) + 7pn−1

32 (p−1).

Using lemma 3.1 to obtain In1 = 12[−pn−1+

pn−1(16pn+7p7)

4 ] and Rn−1 = − 1 2[p

n−1+

pn−1(16pn+7p7)

4 ]and so In−2=Rn−2=In−3=Rn−3=...=0.

Relations for Qi+jand Hi+jcan be derived by using lemma3.2and the fact that P8pj(α8p j

) =1.

4.

PRIMITIVE IDEMPOTENTSCORRESPONDING TOPt pi,t=2,4, 2λ, 4λ,

2µ,2ν, 2g,4g,2λg, 4λg,2µg, 2νg

For 0≤ j≤n−1, we define

Cj= pj

sεΩ2

λgp j

αs, Fj = pj

sεΩ2gp j

αs, Gj = pj

sεΩ4gp j

αs, Kj = pj

sεΩ2

λp j

αs, Oj = pj

sεΩ2p j

αs,

Pj= pj

sεΩ4p j

αs. Due to similar procedure as in section 3, we obtainedCj, Fj, Gj, Kj, Oj, Pj

∈GF(q).

Lemma 4.1. For0≤ j≤n−1, Kj−βp j

Oj=0; Cj−βgp j

Fj=0whereβ =α4pn.

Proof. Since α2λp

j

=α2(1+2p

n)pj

= α2p

j

βp

j

. So Kj = pj

sεΩλpi

α2s = pj[α2λp

i

+α2qλp

i

+

α2q2λpi+...+α2q

φ(pn−j)

2 −1λpi

] =pj[α2piβpi+α2qpiβpi+α2q2piβpi+...+α2piq

φ(pn−j)

2 −1

βpi] =

βp

i

[pj

sεΩ2p j

αs] =βp

i

Oj.

(9)

Proof of lemma4.2−4.4can be computed on similar lines as that of Lemma3.5and represent

Ci+j, Fi+j, Gi+j, Ki+j, Oi+j, Pi+j.

Lemma 4.2. For0≤i≤n;0≤ j≤n−1

sεΩ2p j αλgp

is

=

sεΩ2p j αξgp

is

=

sεΩ2

λp j

αηgp

is

=

sεΩ2

µp j

ανgp

is

=

sεΩ2

µp j

αχgp

is

=

sεΩ2

νp j

αρgp

is

=−

sεΩ2p j ανgp

is

=−

sεΩ2p j αχgp

is

=−

sεΩ2

λp j

αµgp

is

=−

sεΩ2

λp j

αρgp

is

=−

sεΩ2

µp j

αξgp

is

=−

sεΩ2

νp j

αηgp

is =               

φ(pn−j) 4 {α

6gpi+j

+α10gpi

+j

}, i f i+j≥n, g6=1,

1

pjCi+j, i f i+j≤n−1, g6=1,

φ(pn−j) 4 {α

6pi+j

+α10pi

+j

}, i f i+j≥n, g=1,

1

pjKi+j, i f i+j≤n−1, g=1.

Lemma 4.3. For0≤i≤n; 0≤ j≤n−1

sεΩp j α2gp

is

=

sεΩ2λp j αλgp

is

=

sεΩ2λp j αξgp

is

=

sεΩ2µp j αρgp

is

=

sεΩ2νp j αχgp

is

=

sεΩ2λp j ανgp

is

= −

sεΩ2λp j αχgp

is

= −

sεΩ2µp j αηgp

is

= −

sεΩ2νp j αξgp

is =               

φ(pn−j) 4 {α

2gpi+j+

α14gp

i+j

}, i f i+j≥n, g6=1,

1

pjFi+j, i f i+j≤n−1,g6=1,

φ(pn−j) 4 {α

2pi+j+

α14p

i+j

}, i f i+j≥n, g=1,

1

pjOi+j, i f i+j≤n−1,g=1.

Lemma 4.4. For0≤i≤n; 0≤ j≤n−1

sεΩp j α4gp

is

=

sεΩ4

λp j

αλgp

is

=

sεΩ4

λp j

ανgp

is

=

sεΩ4

λp j

αξgp

is

=

sεΩ4

λp j

αχgp

is

=

sεΩ2

λp j

α2νgp

is

=

sεΩ2

µp j

α2µgp

is

=

sεΩ2

νp j

α2νgp

is

=−

sεΩ4

λp j

αµgp

is

=−

sεΩ4

λp j

αηgp

is

=−

sεΩ4

λp j

αρgp

is

=−

sεΩ2

λp j

α2µgp

is =               

φ(pn−j)

4 {α4gp i+j

+α12gpi+j}, i f i+j≥n, g6=1,

1

pjGi+j, i f i+j≤n−1, g6=1,

φ(pn−j)

4 {α4p i+j

+α12pi+j}, i f i+ j≥n, g=1,

1

(10)

Theorem 4.5. When p≡1(mod8), the expressions for the primitive idempotents corresponding to P2pi,P4pi, P2λpi, P4λpi, P2µpi, P2νpi, P2gpi, P4gpi, P2λgpi, P4λgpi, P2µgpi and P2νgpi are given by

P2pj(x) = 161pn[

φ(pn−j)

2 {

t∈A0

(−1)tα2λt p

n+j

Ct pn} + φ(

pn−j)

2

n−1

i=n−j

{

a∈A

(−1)a{α2λap

i+j

Capi +

α2λagp

i+j

Cagpi}} +

1 pj

n−j−1

i=0

{−Ki+jCpi − Pi+jC2pi + Qi+jC4pi + Ri+jC8pi + Ri+jC16pi −

Oi+jCλpi+Pi+jC2λpi+Qi+jC4λpi+Ki+jCµpi−Pi+jC2µpi+Oi+jCνpi+Pi+jC2νpi−Ki+jCηpi−

Oi+jCξpi+Ki+jCρpi+Oi+jCχpi−Ci+jCgpi−Gi+jC2gpi+Hi+jC4gpi+Ii+jC8gpi+Ii+jC16gpi−

Fi+jCλgpi +Gi+jC2λgpi+Hi+jC4λgpi +Ci+jCµgpi−Gi+jC2µgpi +Fi+jCνgpi +Gi+jC2νgpi−

Ci+jCηgpi−Fi+jCξgpi+Ci+jCρgpi+Fi+jCχgpi}]

P4pj(x) = 161pn[

φ(pn−j) 2 {

t∈A0

(−1)tα4t p

n+j

Ct pn} + φ

(pn−j)

2

n−1

i=n−j

{

a∈A

(−1)a{α4ap

i+j

Capi +

α4agp

i+j

Cagpi}} +

1 pj

n−j−1

i=0

{−Pi+jCpi + Qi+jC2pi + Ri+jC4pi + Ri+jC8pi + Ri+jC16pi +

Pi+jCλpi+Qi+jC2λpi+Ri+jC4λpi−Pi+jCµpi+Qi+jC2µpi+Pi+jCνpi+Qi+jC2νpi−Pi+jCηpi+

Pi+jCξpi−Pi+jC

ρpi+Pi+jCχpi−Gi+jCgpi+Hi+jC2gpi+Ii+jC4gpi+Ii+jC8gpi+Ii+jC16gpi+

Gi+jCλgpi+Hi+jC2λgpi+Ii+jC4λgpi −Gi+jCµgpi+Hi+jC2µgpi+Gi+jCνgpi +Hi+jC2νgpi−

Gi+jCηgpi+Gi+jCξgpi−Gi+jCρgpi+Gi+jCχgpi}]

P2λpj(x) = 1 16pn[

φ(pn−j)

2 {

t∈A0

(−1)tα2t p

n+j

Ct pn} +

φ(pn−j)

2

n−1

i=n−j

{

a∈A

(−1)a{α2ap

i+j

Capi +

α2agp

i+j

Cagpi}} +

1 pj

n−j−1

i=0

{−Oi+jCpi + Pi+jC2pi + Qi+jC4pi + Ri+jC8pi + Ri+jC16pi −

Ki+jCλpi−Pi+jC2λpi+Qi+jC4λpi+Oi+jCµpi+Pi+jC2µpi+Ki+jCνpi−Pi+jC2νpi−Oi+jCηpi−

Ki+jCξpi+Oi+jCρpi+Ki+jCχpi−Fi+jCgpi+Gi+jC2gpi+Hi+jC4gpi+Ii+jC8gpi+Ii+jC16gpi−

Ci+jCλgpi−Gi+jC2λgpi+Hi+jC4λgpi+Ci+jCµgpi+Gi+jC2µgpi+Ci+jCνgpi−Gi+jC2νgpi−

Fi+jCηgpi−Ci+jCξgpi+Fi+jCρgpi+Ci+jCχgpi}]

P4λpj(x) = 16p1n[

φ(pn−j)

2 {

t∈A0

α4t p

n+j

Ct pn} + φ(

pn−j)

2

n−1

i=n−j

{

a∈A

(−1)a{α4ap

i+j

Capi +

α4agp

i+j

Cagpi}}

+ 1

pj n−j−1

i=0

{Pi+jCpi+Qi+jC2pi+Ri+jC4pi+Ri+jC8pi+Ri+jC16pi−Pi+jC

(11)

Ri+jC4λpi+Pi+jCµpi+Qi+jC2µpi−Pi+jCνpi+Qi+jC2νpi+Pi+jCηpi−Pi+jCξpi+Pi+jCρpi−

Pi+jCχpi + Gi+jCgpi + Hi+jC2gpi + Ii+jC4gpi + Ii+jC8gpi + Ii+jC16gpi − Gi+jCλgpi +

Hi+jC2λgpi +Ii+jC4λgpi+Gi+jCµgpi +Hi+jC2µgpi −Gi+jCνgpi+Hi+jC2νgpi +Gi+jCηgpi−

Gi+jCξgpi+Gi+jCρgpi−Gi+jCχgpi}]

P2µpj(x) = 16p1n[

φ(pn−j) 2 {

t∈A0

α2λt p

n+j

Ct pn} + φ

(pn−j)

2

n−1

i=n−j

{

a∈A

(−1)a{α2λap

i+j

Capi +

α2λagp

i+j

Cagpi}} +

1 pj

n−j−1

i=0

{Ki+jCpi − Pi+jC2pi + Qi+jC4pi + Ri+jC8pi + Ri+jC16pi +

Oi+jCλpi+Pi+jC2λpi+Qi+jC4λpi−Ki+jCµpi−Pi+jC2µpi−Oi+jCνpi+Pi+jC2νpi+Ki+jCηpi+

Oi+jCξpi−Ki+jCρpi−Oi+jCχpi+Ci+jCgpi−Gi+jC2gpi+Hi+jC4gpi+Ii+jC8gpi+Ii+jC16gpi+

Fi+jCλgpi +Gi+jC2λgpi+Hi+jC4λgpi −Ci+jCµgpi−Gi+jC2µgpi −Fi+jCνgpi +Gi+jC2νgpi+

Ci+jCηgpi+Fi+jCξgpi−Ci+jCρgpi−Fi+jCχgpi}]

P2νpj(x) = 1 16pn[

φ(pn−j)

2 {

t∈A0

α2t p

n+j

Ct pn} + φ

(pn−j)

2

n−1

i=n−j

{

a∈A

(−1)a{α2ap

i+j

Capi +

α2agp

i+j

Cagpi}}+

1 pj

n−j−1

i=0

{Oi+jCpi+Pi+jC2pi+Qi+jC4pi+Ri+jC8pi+Ri+jC16pi+Ki+jCλpi−

Pi+jC2λpi+Qi+jC4λpi−Oi+jCµpi+Pi+jC2µpi−Ki+jCνpi−Pi+jC2νpi+Oi+jCηpi+Ki+jCξpi−

Oi+jCρpi−Ki+jCχpi+Fi+jCgpi+Gi+jC2gpi+Hi+jC4gpi+Ii+jC8gpi+Ii+jC16gpi+Ci+jCλgpi−

Gi+jC2λgpi+Hi+jC4λgpi−Fi+jCµgpi+Gi+jC2µgpi −Ci+jCνgpi −Gi+jC2νgpi+Fi+jCηgpi+

Ci+jCξgpi−Fi+jCρgpi−Ci+jCχgpi}], where

Pn1 = 18[4p−p2(n−1) + p

pn−1(−16pn−17p+7)] , G

n−1 = −18[4

p

−p2(n−1) −

p

pn−1(−16pn−17p+7)] and C

i+j, Fi+j, Ki+j, Oi+j can be obtained, from the

fol-lowing relations,

1 pj

n−j−1

i=0

{Ki+jFi+j+Oi+jCi+j

pi }=−

pn−1(p−1)

2 +

9pn−j−1(p−1)

32 ,

1 pj

n−j−1

i=0

{Ki+jOi+j+Ci+jFi+j

pi }=−

pn−1

4 (p−1)−

7pn−j−1(p−1)

32 ,

1 pj

n−j−1

i=0

{Ki+jCi+j+Oi+jFi+j

pi }=−

pn−j−1(p−1)

16 ,

1 pj

n−j−1

i=0

{K

2

i+j+C2i+j+F2i+j+O2i+j

pi }=−p

(n−1)

+ p

n−j−1(p1)

8 .

(12)

P, Q, R, K, O by G, H, I, C, F andαupi

+j

byαugpi

+j

respectively in the expression of P2pj, P4pj,

P2λpj, P4λpj, P2µpj and P2νpj.

Proof. These expressions can be obtained using Lemmas3.3−3.6,4.2−4.4and similar proce-dure as in theorem3.7. Also the relations can be derived using P2pj(α2p

i

) =1, P2pj(α2gp

i

) =0,

P2pj(α2λp j

) =0and P2pj(α2νgp j

) =0.

5.

PRIMITIVE IDEMPOTENTSCORRESPONDING TOPt pi,t=1,λ,µ,ν,η,ξ,ρ,

χ,g,λg,µg,νg,ηg,ξg,ρg,χg

For 0≤ j ≤n−1, define Aj = pj

sεΩgp j

αs; Bj = pj

sεΩ

λgp j

αs ; Dj = pj

sεΩ

µgp j

αs ; Ej =

pj

sεΩ

νgp j

αs;Jj=pj

sεΩ

λp j

αs;Lj=pj

sεΩ

µp j

αs;Mj=pj

sεΩ

νp j

αs;Nj=pj

sεΩp j

αs.

Using similar procedure as in section 3 we obtainAj,Bj,Dj,Ej,Jj,Lj,Mj,Nj∈GF(q).

Proof of lemma 5.1 is similar to that of lemma 4.1.

Lemma 5.1. For 0≤ j ≤n−1, Lj−βp j

Nj =0; Mj−βp j

Jj =0; Dj−βgp j

Aj = 0; Ej−

βgp

j

Bj=0.

Proof of Lemma 5.2−5.5 is similarly as that of lemma 3.5.

Lemma 5.2. For0≤i≤n; 0≤ j≤n−1

sεΩp j αgp

is

=

sεΩ

λp j

αξgp

is

=

sεΩ

µp j

αρgp

is

=

sεΩ

νp j

ανgp

is

=

sεΩ

ηp j

αηgp

is

=

sεΩ

χp j

αχgp

is

=−

sεΩ

νp j

αχgp

is

=−

sεΩ

λp j

αλgp

is

=−

sεΩ

µp j

αµgp

is

=−

sεΩ

ξp j

αξgp

is

=−

sεΩ

ρp j

αρgp

is =               

φ(pn−j) 4 {αgp

i+j

+α7gpi+j}, i f i+j≥n, g6=1,

1

pjAi+j, i f i+j≤n−1, g6=1,

φ(pn−j) 4 {αp

i+j

+α7pi

+j

}, i f i+j≥n, g=1,

1

pjNi+j, i f i+j≤n−1, g=1.

Lemma 5.3. For0≤i≤n; 0≤ j≤n−1

sεΩp j αλgp

is

=

sεΩ

ηp j

αξgp

is

=

sεΩ

µp j

ανgp

is

=

sεΩ

ρp j

αχgp

is

=−

sεΩp j αξp

is

=−

sεΩ

νp j

αρgp

(13)

=−

sεΩ

λp j

αηgp

is

=−

sεΩ

µp j

αχgp

is =               

φ(pn−j)

4 {α3gp i+j

+α5gpi+j}, i f i+j≥n, g6=1,

1

pjBi+j, i f i+j≤n−1, g6=1,

φ(pn−j)

4 {α3p i+j

+α5pi+j}, i f i+ j≥n, g=1,

1

pjJi+j, i f i+j≤n−1, g=1.

Lemma 5.4. For0≤i≤n; 0≤ j≤n−1

sεΩp j αµgp

is

=

sεΩ

λp j

ανgp

is

=

sεΩ

ηp j

αρgp

is

=

sεΩ

ξp j

αχgp

is

=−

sεΩp j αρgp

is

=−

sεΩ

λp j

αχgp

is

=−

sεΩ

µp j

αηgp

is

=−

sεΩ

νp j

αξgp

is =               

φ(pn−j)

4 {α3gp i+j

+α5gpi+j}, i f i+j≥n, g6=1,

1

pjDi+j, i f i+ j≤n−1, g6=1,

φ(pn−j) 4 {α3p

i+j

+α5pi+j}, i f i+j≥n, g=1,

1

pjLi+j, i f i+ j≤n−1, g=1.

Lemma 5.5. For0≤i≤n;0≤ j≤n−1

sεΩp j ανgp

is

=

sεΩ

λp j

αρgp

is

=

sεΩ

µp j

αξgp

is

=

sεΩ

ηp j

αχgp

is

=−

sεΩp j αχgp

is

=−

sεΩ

λp j

αµgp

is

=−

sεΩ

νp j

αηgp

is

=−

sεΩ

ξp j

αρgp

is =               

φ(pn−j) 4 {αgp

i+j

+α7gpi+j}, i f i+ j≥n, g6=1,

1

pjEi+j, i f i+j≤n−1, g6=1,

φ(pn−j) 4 {αp

i+j

+α7pi+j}, i f i+j≥n, g=1,

1

pjMi+j, i f i+ j≤n−1, g=1.

Theorem 5.6. For p≡1(mod8), the expressions for the primitive idempotents corresponding to Ppi, P

λpi,Pµpi,Pνpi,Pηpi,Pξpi,Pρpi,Pχpi,Pgpi,Pλgpi,Pµgpi,Pνgpi,Pηgpi,Pξgpi,Pρgpi and Pχgpi are

given by

Ppj(x) = 1 16pn[

φ(pn−j)

2 {

t∈A0

(−1)tαtνp

n+j

Ct pn} + φ(

pn−j)

2

n−1

i=n−j

{

a∈A

(−1)a{αaνp

i+j

Capi +

αaνgp

i+j

Cagpi}} +

1 pj

n−j−1

i=0

{−Mi+jCpi − Ki+jC2pi − Pi+jC4pi + Qi+jC8pi + Ri+jC16pi −

Li+jCλpi−Oi+jC2λpi+Pi+jC4λpi−Ji+jCµpi+Ki+jC2µpi−Ni+jCνpi+Oi+jC2νpi+Mi+jCηpi+

Li+jCξpi+Ji+jCρpi+Ni+jCχpi−Ei+jCgpi−Ci+jC2gpi−Gi+jC4gpi+Hi+jC8gpi+Ii+jC16gpi−

Di+jCλgpi −Fi+jC2λgpi +Gi+jC4λgpi −Bi+jCµgpi +Ci+jC2µgpi −Ai+jCνgpi +Fi+jC2νgpi+

(14)

Pλpj(x) = 1 16pn[

φ(pn−j) 2 {

t∈A0

(−1)tαtµp

n+j

Ct pn} + φ

(pn−j)

2

n−1

i=n−j

{

a∈A

(−1)a{αaµp

i+j

Capi +

αaµgp

i+j

Cagpi}} +

1 pj

n−j−1

i=0

{−Li+jCpi − Oi+jC2pi + Pi+jC4pi + Qi+jC8pi + Ri+jC16pi +

Mi+jCλpi−Ki+jC2λpi−Pi+jC4λpi+Ni+jCµpi+Oi+jC2µpi−Ji+jCνpi+Ki+jC2νpi+Li+jCηpi−

Mi+jCξpi−Ni+jCρpi+Ji+jCχpi−Di+jCgpi−Fi+jC2gpi+Gi+jC4gpi+Hi+jC8gpi+Ii+jC16gpi+

Ei+jCλgpi −Ci+jC2λgpi−Gi+jC4λgpi+Ai+jCµgpi +Fi+jC2µgpi −Bi+jCνgpi +Ci+jC2νgpi +

Di+jCηgpi−Ei+jCξgpi−Ai+jCρgpi+Bi+jCχgpi}]

Pµpj(x) = 1 16pn[

φ(pn−j)

2 {

t∈A0

(−1)tαλt p

n+j

Ct pn} + φ(p n−j)

2

n−1

i=n−j

{

a∈A

(−1)a{αaλp

i+j

Capi +

αaλgp

i+j

Cagpi}} +

1 pj

n−j−1

i=0

{−Ji+jCpi + Ki+jC2pi − Pi+jC4pi + Qi+jC8pi + Ri+jC16pi +

Ni+jCλpi+Oi+jC2λpi+Pi+jC4λpi+Mi+jCµpi−Ki+jC2µpi−Li+jCνpi−Oi+jC2νpi+Ji+jCηpi−

Ni+jCξpi−Mi+jCρpi+Li+jCχpi−Bi+jCgpi+Ci+jC2gpi−Gi+jC4gpi+Hi+jC8gpi+Ii+jC16gpi+

Ai+jCλgpi +Fi+jC2λgpi +Gi+jC4λgpi +Ei+jCµgpi −Ci+jC2µgpi −Di+jCνgpi −Fi+jC2νgpi+

Bi+jCηgpi−Ai+jCξgpi−Ei+jCρgpi+Di+jCχgpi}]

Pνpj(x) = 1 16pn[

φ(pn−j)

2 {

t∈A0

(−1)tαt p

n+j

Ct pn} + φ(

pn−j)

2

n−1

i=n−j

{

a∈A

(−1)a{αap

i+j

Capi +

αagp

i+j

Cagpi}} +

1 pj

n−j−1

i=0

{−Ni+jCpi + Oi+jC2pi + Pi+jC4pi + Qi+jC8pi + Ri+jC16pi −

Ji+jCλpi+Ki+jC2λpi−Pi+jC4λpi−Li+jCµpi−Oi+jC2µpi−Mi+jCνpi−Ki+jC2νpi+Ni+jCηpi+

Ji+jCξpi+Li+jCρpi+Mi+jCχpi−Ai+jCgpi+Fi+jC2gpi+Gi+jC4gpi+Hi+jC8gpi+Ii+jC16gpi−

Bi+jCλgpi +Ci+jC2λgpi −Gi+jC4λgpi −Di+jCµgpi −Fi+jC2µgpi −Ei+jCνgpi −Ci+jC2νgpi+

Ai+jCηgpi+Bi+jCξgpi+Di+jCρgpi+Ei+jCχgpi}]

Pηpj(x) = 161pn i+j[

φ(pn−j)

2 {

t∈A0

αtνp

n+j

Ct pn} + φ(

pn−j)

2

n−1

i=n−j

{

a∈A

αaνp

i+j

Capi +

a∈A

αaνgp

i+j

Cagpi} +

1 pj

n−j−1

i=0

{Mi+jCpi − Ki+jC2pi − Pi+jC4pi + Qi+jC8pi + Ri+jC16pi +

Li+jCλpi−Oi+jC2λpi+Pi+jC4λpi+Ji+jCµpi+Ki+jC2µpi+Ni+jCνpi+Oi+jC2νpi−Mi+jCηpi−

Li+jCξpi−Ji+jCρpi−Ni+jCχpi+Ei+jCgpi−Ci+jC2gpi−Gi+jC4gpi+Hi+jC8gpi+Ii+jC16gpi+

Di+jCλgpi −Fi+jC2λgpi +Gi+jC4λgpi +Bi+jCµgpi +Ci+jC2µgpi +Ai+jCνgpi +Fi+jC2νgpi−

(15)

Pξpj(x) = 1 16pn[

φ(pn−j) 2 {

t∈A0

αtµp

n+j

Ct pn} + φ

(pn−j)

2

n−1

i=n−j

{

a∈A

{αaµp

i+j

Capi +

αaµgp

i+j

Cagpi}} +

1 pj

n−j−1

i=0

{Li+jCpi − Oi+jC2pi + Pi+jC4pi + Qi+jC8pi + Ri+jC16pi −

Mi+jCλpi−Ki+jC2λpi−Pi+jC4λpi−Ni+jCµpi+Oi+jC2µpi+Ji+jCνpi+Ki+jC2νpi−Li+jCηpi+

Mi+jCξpi+Ni+jCρpi−Ji+jCχpi+Di+jCgpi−Fi+jC2gpi+Gi+jC4gpi+Hi+jC8gpi+Ii+jC16gpi−

Ei+jCλgpi −Ci+jC2λgpi−Gi+jC4λgpi−Ai+jCµgpi +Fi+jC2µgpi +Bi+jCνgpi +Ci+jC2νgpi −

Di+jCηgpi+Ei+jCξgpi+Ai+jCρgpi−Bi+jCχgpi}]

Pρpj(x) = 1 16pn[

φ(pn−j)

2 {

t∈A0

αtλp

n+j

Ct pn} + φ(p n−j)

2

n−1

i=n−j

{

a∈A

αaλp

i+j

Capi +

a∈A

αaλgp

i+j

Cagpi} +

1 pj

n−j−1

i=0

{Ji+jCpi + Ki+jC2pi − Pi+jC4pi + Qi+jC8pi + Ri+jC16pi −

Ni+jCλpi+Oi+jC2λpi+Pi+jC4λpi−Mi+jCµpi−Ki+jC2µpi+Li+jCνpi−Oi+jC2νpi−Ji+jCηpi+

Ni+jCξpi+Mi+jCρpi−Li+jCχpi+Bi+jCgpi+Ci+jC2gpi−Gi+jC4gpi+Hi+jC8gpi+Ii+jC16gpi−

Ai+jCλgpi +Fi+jC2λgpi +Gi+jC4λgpi −Ei+jCµgpi −Ci+jC2µgpi +Di+jCνgpi −Fi+jC2νgpi−

Bi+jCηgpi+Ai+jCξgpi+Ei+jCρgpi−Di+jCχgpi}]

Pχpj(x) = 16p1n[

φ(pn−j) 2 {

t∈A0

αt p

n+j

Ct pn} + φ

(pn−j)

2

n−1

i=n−j

{

a∈A

αap

i+j

Capi +

a∈A

αagp

i+j

Cagpi} +

1 pj

n−j−1

i=0

{Ni+jCpi + Oi+jC2pi + Pi+jC4pi + Qi+jC8pi + Ri+jC16pi +

Ji+jCλpi+Ki+jC2λpi−Pi+jC4λpi+Li+jCµpi−Oi+jC2µpi+Mi+jCνpi−Ki+jC2νpi−Ni+jCηpi−

Ji+jCξpi−Li+jCρpi−Mi+jCχpi+Ai+jCgpi+Fi+jC2gpi+Gi+jC4gpi+Hi+jC8gpi+Ii+jC16gpi+

Bi+jCλgpi +Ci+jC2λgpi −Gi+jC4λgpi +Di+jCµgpi −Fi+jC2µgpi +Ei+jCνgpi −Ci+jC2νgpi−

Ai+jCηgpi−Bi+jCξgpi−Di+jCρgpi−Ei+jCχgpi}]

The expressions for Pgpj, P

λgpj, Pµgpj, Pνgpj, Pηgpj, Pξgpj, Pρgpj and Pχgpj can be computed

by interchanging P, Q, R, K, O, L, M, N, J by G, H, I, C, F, D, E, A, B andαupi+j byαugpi+j

respectively, Where Ai+j, Bi+j, Di+j, Ei+j, Ji+j, Li+j, Mi+j, Ni+jcan be computed, using lemma

5.1and the following relations,

1 pj

n−j−1

i=0

{Mi+jNi+j+Ai+jEi+j+Ji+jLi+j+Bi+jDi+j

pi }=−

5pn−1(p+1)

4 −

7pn−j−1(p−1)

16 ,

1 pj

n−j−1

i=0

{Mi+jBi+j+Ni+jDi+j−Ji+jEi+j−Ai+jLi+j

pi }=

3pn−j−1(p−1)

(16)

1 pj

n−j−1

i=0

{M

2

i+j+E2i+j+L2i+j+D2i+j+J2i+j+B2i+j+N2i+j+A2i+j

pi }

=−2p(n−1) + p

n−j−1(p1)(3+4α6pn+j+4α2pn+j)

8 ,

1 pj

n−j−1

i=0

{Ei+jLi+j+Ji+jAi+j−Mi+jDi+j−Ni+jBi+j

pi }

=pn−1(p−1) +5p

n−j−1(p1)

8 +

pn−j−1(p−1)(α3(χ+µg)pn+jα(ν+µg)pn+j)

4 .

Proof. The above expressions can be obtained using Lemmas3.3−3.6,4.2−4.4and5.2−5.5 and similar procedure as in theorem3.7. Also the relations can be derived using Ppj(αp

i

) =1,

Ppj(αλgp i

) =0, Ppj(ανp

j

) =0and Pλpj(αµgp j

) =0.

6.

DIMENSION ANDGENERATINGPOLYNOMIALS

The polynomialms(x) =

sεΩs

(x−αs)denote the minimal polynomial for αs and the

gener-ating polynomial for cyclic code Ms of length 16pn corresponding to the cyclotomic coset Ωs

is x16mspn(x)−1 and the dimension of Ms is equal to the cardinality of the class Ωs by J. Singh and

Arrora.

Theorem 6.1. (i) The generating polynomial for the codes Mt pn, for t ∈A0 are (1+x+

x2+...+x(16pn−1)), (x8−1)(x2+β2)(x2−β6)(x+β)(x+β7)(1+x16 +...+x16(pn−1)),

(x+β2)(x−β6)(x4−1)(x8+1)(1+x16+...+x16(p

n1)

),(x+β3)(x+β5)(x2−β2)(x8−1)(1+

x16+...+x16(pn−1)), (x2−1)(x4+1)(x8+1)(1+x16+...+x16(pn−1)), (x8+1)(x4−1)(x−

β2)(x+β6)(1+x16+...+x16(p

n1)

),(x8+1)(x4+1)(x2+1)(x−1)(1+x16+...+x16(pn−1)),

(x8−1)(x2−β6)(x2+β2)(x−β7)(x−β)(1+x16+...+x16(pn−1))and(x8−1)(x2+β6)(x2−

β2)(x−β3)(x−β5)(1+x16+...+x16(pn−1))respectively, whereβ is16th root of unity.

(ii) The generating polynomial for M8pi⊕M8gpi, M16pi⊕M16gpi and Mpi⊕M2pi⊕M4pi⊕

Mλpi⊕M2λpi⊕M4λpi⊕Mµpi⊕M2µpi⊕Mνpi⊕M2νpi⊕Mηpi⊕Mξpi⊕Mρpi⊕Mχpi⊕Mgpi⊕

M2gpi⊕M4gpi⊕Mλgpi⊕M2λgpi⊕M4λgpi⊕Mµgpi⊕M2µgpi⊕Mνgpi⊕M2νgpi⊕Mηgpi⊕Mξgpi⊕

Mρgpi⊕Mχgpi are(xp n−i−1

+1)(xpn−i−1)(x2pn−i+1)(x4pn−i+1)(x8pn−i+1)(1+x16pn−i+...+

x16pn−i(pi−1)),(xpn−i−1−1)(xpn−i+1)(x2pn−i+1)(x4pn−i+1)(x8pn−i+1)(x8pn−i+1)(1+x16pn−i+

...+x16pn−i(pi−1)) and (x2pn−i−1+1)(x4pn−i−1+1)(x8pn−i−1+1)(x2pn−i−1)(1+x16pn−i+...+

(17)

Proof. (i)The minimal polynomial forαt p

n

, fort∈A0are(x−1),(x−β)(x−β7),(x−β2)(x+ β6),(x−β3)(x−β5),(x2+1),(x−β6)(x+β2),(x+1),(x+β)(x+β7)and(x+β3)(x+β5),

respectively. The corresponding generating polynomials are (1+x+x2+...+x(16pn−1)),

(x8−1)(x2+β2)(x2−β6)(x+β)(x+β7)(1+x16 +...+x16(pn−1)), (x8+1)(x4−1)(x+

β2)(x−β6)(1+x16+...+x16(p

n1)

), (x8−1)(x2+β6)(x+β3)(x2−β2)(x+β5)(1+x16+

...+x16(pn−1)),(x2−1)(x4+1)(x8+1)(1+x16+...+x16(pn−1)),(x8+1)(x4−1)(x−β2)(x+ β6)(1+x16+...+x16(p

n1)

), (x8+1)(x4+1)(x2+1)(x−1)(1+x16+...+x16(pn−1)), (x8− 1)(x2−β6)(x−β7)(x−β)(x2+β2)(1+x16+...+x16(pn−1)), (x8−1)(x−β3)(x−β5)(x2+ β6)(x2−β2)(1+x16+...+x16(p

n1)

).

(ii) The product of minimal polynomial satisfied by α8pi and α8gpi is ( x

pn−i+1

xpn−i−1+1).

There-fore, the generating polynomial forM8pi⊕M8gpi is(xp n−i−1

+1)(xpn−i−1)(x2pn−i+1)(x4pn−i+

1)(x8pn−i+1)(1+x16pn−i+...+x16pn−i(pi−1)). The product of minimal polynomial satis-fied by α16pi and α16gpi is ( xpn

−i

−1

xpn−i−11). Therefore, the generating polynomial for M16pi⊕

M16gpi is (xp n−i−1

−1)(xpn−i+1)(x2pn−i+1)(x4pn−i+1)(x8pn−i+1)(x8pn−i+1)(1+x16pn−i+

...+x16pn−i(pi−1)). Also the product of minimal polynomial satisfied by αpi, α2pi, α4pi,..., αρgpi, αχgpi is (x

2pn−i+1)(x4pn−i+1)(x8pn−i+1)

(x2pn−i−1+1)(x4pn−i−1+1)(x8pn−i−1+1). Therefore, the generating polynomial for

Mpi⊕M2pi⊕M4pi⊕Mλpi⊕M2λpi⊕M4λpi⊕Mµpi⊕M2µpi⊕Mνpi⊕M2νpi⊕Mηpi⊕Mξpi⊕

Mρpi⊕Mχpi⊕Mgpi⊕M2gpi⊕M4gpi⊕Mλgpi⊕M2λgpi⊕M4λgpi⊕Mµgpi⊕M2µgpi⊕Mνgpi⊕

M2νgpi⊕Mηgpi⊕Mξgpi⊕Mρgpi⊕Mχgpi is (x2p n−i−1

+1)(x4pn−i−1 +1)(x8pn−i−1+1)(x2pn−i−

1)(1+x16pn−i+...+x16pn−i(pi−1)).

7.

MINIMUM DISTANCE

Iflis a cyclic code of lengthmgenerated byg(x)and its minimum distance isd, then the code

¯

l of lengthmkgenerated byg(x)(1+xm+x2m+...+x(k−1)m)is a repetition code ofl repeated ktimes and its minimum distance isdkby Bakshi. Here, we find the minimum distance of the

minimal cyclic codeMs of length 16pn, generated by the primitive idempotentPs.

Theorem 7.1. Each the codes Mt pn,for t∈A0are of minimum distance16pn. For0≤i≤n−1,

(18)

32piand minimum distance for the codes Mapi, Magpi, a∈A− {8,16}are greater than or equal

to16pi.

Proof. As the generating polynomial for the codeM0is a polynomial of length 16pn, hence its minimum distance is 16pn. Also, the generating polynomial for the cyclic code Mpn is (x8−

1)(x2+β2)(x+β)(x2−β6)(x+β7)(1+x16+...+x16(pn−1)). Which the code repeat for the

cyclic code of length 16 with generating polynomial(x8−1)(x2+β2)(x+β)(x2−β6)(x+β7),

repeated pntimes. So its minimum distance is 16pn. Similarly, the minimum distance for each

of the cyclic codesMt pn, where 2≤t≤15 is 16pn.

The cyclic codes M8pi and M8gpi, with genrating polynomial (xp n−i−1

+1)(xpn−i−1)(x2pn−i+

1)(x4pn−i+1)(x8pn−i+1)(1+x16pn−i+...+x16pn−i(pi−1))is a repetition code of the code gener-ated by(xpn−i−1+1)(xpn−i−1)(x2pn−i+1)(x4pn−i+1)(x8pn−i+1)of length 16pn−iand minimum distance 32 repeated pitimes. Therefore its minimum distance is 32pi. The codes

correspond-ing to M8pi and M8gpi are the sub codes of the above codes, so their minimum distances are

greater than or equal to 32pi.

Similarly, the minimum distance for each of the cyclic codesM16pi andM16gpi of length 16pn

are also greater than or equal to 32pi.

The product of generating polynomials for the cyclic codes Mapi, Magpi, a ∈ A− {8,16}

is (x2pn−i−1+1)(x4pn−i−1+1)(x8pn−i−1+1)(x2pn−i+1)(1+x16pn−i+...+x16pn−i(pi−1)). If we consider a code C of length 16pn−i generated by the polynomial (x2pn−i−1+1)(x4pn−i−1+

1)(x8pn−i−1+1)(x2pn−i+1), then the minimum distance for this code is 16. Since the cyclic code of length 16pngenerated by the said polynomial is a repetition of the codeC repeated pi

times. Hence its minimum distance is 16pi.

Since the codes corresponding toΩapi,Ωagpi,a∈Aare the sub codes of the said codes, so their

minimum distance is greater than or equal to 16pi.

8.

EXAMPLE

Example 6.1. Cyclic Codes of length 48.

Take p=3,n=1,q=103. Then the q-cyclotomic cosets are

(19)

Minimal polynomials for αs,α7s where 0≤s≤41 are x−1, x2−2x+47, x2+90x+46,

x2+68x−1, x2−77x+56, x2−54x+57, x2−94x+1, x−47, x2−94x−1, x2+7x+56, x2+3x+57, x2−14x+1, x2−66x+47, x−46, x2−92x+57, x2+20x+1, x2+38x+47, x2−40x+46,x+1,x2+2x+47,x2−90x+46,x2−68x−1,x−56,x2−9x−1,x2+96x+56, x−57 andx2−11x+56 respectively.

The minimal codesM0,M1, M2,M3,M4, M5,M6, M7,M8,M9, M10, M11, M12,M13,M16,M17,

M18,M19,M20,M24,M25,M26,M27,M32,M33,M34,M40 andM41of length 48 are as follows:

Code Dim. Min. Distance Bound Generating Polynomial

M0 1 48

47

t=0

{xt}

M1 1 16≤d≤48 6+46x+61x2+6x3+91x4+41x5+2x6+54x7+

68x8+39x9+55x10 +30x11+79x12 +86x13 +

48x14+55x15+32x16+101x17+8x18+99x19+

15x20+84x21+69x22+91x23+55x24+53x25+

23x26 +13x27+68x28 +7x29+12x30 +42x31+

87x32 +5x33+40x34 +52x35+43x36 +84x37+

18x38+45x39+87x40+40x41+13x42+26x43+

60x44+2x45+x46

M2 1 16≤d≤48 42+14x+12x2+21x3+93x4+93x5+78x6+

76x7+78x8+101x9+47x10+29x11+43x12 +

16x13+73x14+27x15+15x16+35x17+23x18+

55x19 +24x20+75x21 +5x22+58x23 +23x24+

3x25 +72x26+27x27 +71x28+15x29 +43x30+

79x31+102x32+101x33+42x34+97x35+78x36+

58x37+55x38+21x39+54x40+26x41+42x42+

References

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