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http://www.newtheory.org
ISSN: 2149-1402
Received : 10.03.2015
Accepted : 13.05.2015
Year : 2015, Number : 5, Pages: 13-18
Original Article **
SOME INEQUALITIES FOR q AND (q, k)
DEFORMED GAMMA FUNCTIONS
Kwara Nantomah1,*
Osman Kasimu2
1,2
< [email protected]>
<[email protected]>
Department of Mathematics, Faculty of Mathematical Sciences, University for Development
Studies, Navrongo Campus, P. O. Box 24, Navrongo, UE/R, Ghana.
Abstract − In this short paper, the authors establish some inequalities involving the q and (q, k)
deformed Gamma functions by employing some basic analytical techniques.
Keywords − Gamma function, q-deformation, (q, k)-deformation, q-addition, inequality.
1
Introduction
Let Γ(x) be the classical Gamma function and ψ(x) be the classical Psi or Digamma function defined
for x ∈ R+ as:
Z ∞
Γ(x) =
tx−1 e−t dt,
0
d
Γ0 (x)
ln Γ(x) =
.
dx
Γ(x)
It is common knowledge in literature that the Gamma function satisfies the following properties.
ψ(x) =
Γ(n + 1) = n!,
n ∈ Z +,
Γ(x + 1) = xΓ(x),
x ∈ R+ .
Also, let Γq (x) be the q-deformed Gamma function (also known as the q-Gamma function or the qanalogue of the Gamma function) and ψq (x) be the q-deformed Psi function defined for q ∈ (0, 1) and
x ∈ R+ as (See [6], [7] and the references therein):
Γq (x) = (1 − q)1−x
**
*
∞
Y
1 − qn
1 − q x+n
n=1
and ψq (x) =
Edited by Erhan Set and Naim Cagman (Editor-in-Chief ).
Corresponding Author.
d
ln Γq (x)
dx
14
Journal of New Theory 5 (2015) 13-18
with Γq (x) satisfying the properties:
Γq (n + 1) = [n]q !
n ∈ Z +,
Γq (x + 1) = [x]q Γq (x)
where [x]q =
x
1−q
1−q
(1)
+
x∈R .
(2)
and [x + y]q = [x]q + q x [y]q for x, y ∈ R+ . See [2].
Similarly, let Γ(q,k) (x) be the (q, k)-deformed Gamma function and ψ(q,k) (x) be the (q, k)-deformed
Psi function defined for q ∈ (0, 1), k > 0 and x ∈ R+ as (See [2], [8], [10] and the references therein):
x
Γ(q,k) (x) =
where (x + y)nq,k =
−1
k
(1 − q k )q,k
(1 − q)
Qn−1
j=0 (x
=
x
k −1
(1 − q k )∞
q,k
(1 −
q x )∞
q,k .(1
− q)
x
k −1
and
ψ(q,k) (x) =
d
ln Γ(q,k) (x)
dx
+ q jk y) with Γ(q,k) (x) satisfying the following property:
Γ(q,k) (x + k) = [x]q Γ(q,k) (x),
x ∈ R+ .
(3)
The q-addition (otherwise known as the q-analogue or q-deformation of the ordinary addition) can be
defined in the following two ways:
The Nalli-Ward-Alsalam q-addition, ⊕q is defined (See [11], [1], [3]) as:
n µ ¶
X
n
(a ⊕q b)n :=
ak bn−k for a, b ∈ R, n ∈ N.
k q
(4)
k=1
where
¡n¢
k q
:=
[n]q !
[k]q ![n−k]q !
is the q-binomial coefficient.
The Jackson-Hahn-Cigler q-addition, ¢q is defined (See [4], [5], [3]) as:
n µ ¶
X
k(k−1)
n
(a ¢q b)n :=
q 2 an−k bk for a, b ∈ R, n ∈ N.
k q
(5)
k=1
Notice that both ⊕q and ¢q reduce to the ordinary addition, + when q = 1.
In a recent paper [9], the inequalities:
Γ(m + n + 1)
(m + n)m+n
<
,
Γ(m + 1)Γ(n + 1)
mm nn
Γ(x + y + 1)
(x + y)x+y
≤
,
Γ(x + 1)Γ(y + 1)
xx y y
m, n ∈ Z +
x, y ∈ R+
(6)
(7)
which occur in the study of probability theory were presented together with some other results. In this
paper, the objective is to establish related inequalities for the q and (q, k) deformed Gamma functions.
The results are presented in the following section.
2
Main Results
Theorem 2.1. Let q ∈ (0, 1) and m, n ∈ Z + . Then, the inequality:
Γq (m + n + 1)
(m ⊕q n)m+n
≤
Γq (m + 1)Γq (n + 1)
mm nn
holds true.
(8)
15
Journal of New Theory 5 (2015) 13-18
Proof. By equation (4) we obtain;
m+n
(m ⊕q n)
µ
¶
m+n
m m nn
≥
m
q
since the binomial expansion of (m ⊕q n)m+n includes the term
terms. That implies,
(m ⊕q n)m+n
[m + n]q !
≤
.
[m]q ![n]q !
m m nn
¡m+n¢
m
q
mm nn as well as some other
Now using relation (1) yields,
Γq (m + n + 1)
(m ⊕q n)m+n
≤
Γq (m + 1)Γq (n + 1)
mm nn
completing the proof.
Theorem 2.2. Let q ∈ (0, 1) and m, n ∈ Z + . Then, the inequality:
Γq (m + n + 1)
(m ¢q n)m+n q
≤
Γq (m + 1)Γq (n + 1)
mm nn
n(1−n)
2
(9)
holds true.
Proof. Similarly, by equation (5) we obtain;
m+n
(m ¢q n)
µ
¶
n(n−1)
m+n
≥
q 2 mm nn .
n
q
Implying,
[m + n]q !
(m ¢q n)m+n q
≤
[m]q ![n]q !
m m nn
n(1−n)
2
.
By relation (1), we obtain;
Γq (m + n + 1)
(m ¢q n)m+n q
≤
Γq (m + 1)Γq (n + 1)
mm nn
n(1−n)
2
concluding the proof.
Lemma 2.3. If q ∈ (0, 1) and x ∈ (0, 1) then,
ln(1 − q x ) − ln(1 − q) < 0.
(10)
Proof. We have q x > q for all q ∈ (0, 1) and x ∈ (0, 1). That implies, 1 − q x < 1 − q. Taking the
logarithm of both sides concludes the proof.
Theorem 2.4. Let q ∈ (0, 1) fixed, x ∈ (0, 1) and y ∈ (0, 1) be such that ψq (x + 1) > 0. Then, the
inequality:
[x+y]q
Γq (x + y + 1)
[x + y]q
≥
(11)
[x]
x
Γq (x + 1)Γq (y + 1)
[x]q q [y]q eq [y]q Γq (y)
holds true.
16
Journal of New Theory 5 (2015) 13-18
Proof. Let Q and T be defined for q ∈ (0, 1) fixed, x ∈ (0, 1) and y ∈ (0, 1) by,
Q(x) =
e[x]q Γq (x + 1)
[x]
[x]q q
and
T (x, y) =
Q(x + y)
.
Q(x)Q(y)
Let µ(x) = ln Q(x). That is,
µ(x) = [x]q + ln Γq (x + 1) − [x]q ln[x]q . Then,
qx
µ(x)0 = ψq (x + 1) + (ln q)
ln[x]q
1−q
qx
(ln(1 − q x ) − ln(1 − q)) > 0
= ψq (x + 1) + (ln q)
1−q
This is as a result of Lemma 2.3 and the fact that ln q < 0 for q ∈ (0, 1). Hence Q(x) is increasing.
Next, we have,
[y]
T (x, y) =
Q(x + y)
Q(x + y) 1
1
[y]q q
=
.
≥
= [y]
Q(x)Q(y)
Q(x) Q(y)
Q(y)
e q [y]q Γq (y)
since Q(x) is increasing and Γq (y + 1) = [y]q Γ(y). That implies,
[x]
T (x, y) =
[y]q
[x]q q [y]q
[x+y]q
[x + y]q
[x]
=
.
Γq (x + y + 1)
e[x+y]q
.
e[x]q +[y]q Γq (x + 1)Γq (y + 1)
.
e[x]q +q [y]q
Γq (x + y + 1)
[y]q q
.
≥
e[x]q +[y]q Γq (x + 1)Γq (y + 1)
e[y]q [y]q Γq (y)
[y]q
[x+y]q
[x + y]q
[y]
x
[x]q q [y]q
yielding the results as in (11).
Γ (x)Γ (y)
q
be the q-deformation of the classical Beta function. Then,
Remark 2.5. Let Bq (x, y) = Γq q (x+y)
inequality (11) can be rearranged as follows.
Bq (x, y) ≤
[x]q −1 q x [y]q
[x]q
e
[x +
Γq (y)
.
[x+y]q −1
y]q
Theorem 2.6. Let q ∈ (0, 1) fixed, k > 0 and x ∈ (0, 1) be such that ψ(q,k) (x + k) > 0. Then, the
inequality:
[x+y]q
Γ(q,k) (x + y + k)
[x + y]q
≥
(12)
[x]
x
Γ(q,k) (x + k)Γ(q,k) (y + k)
[x]q q [y]q eq [y]q Γ(q,k) (y)
is valid.
Proof. Let G and H be defined for q ∈ (0, 1) fixed, k > 0, x ∈ (0, 1) and y ∈ (0, 1) by,
G(x) =
e[x]q Γ(q,k) (x + k)
[x]
[x]q q
and H(x, y) =
G(x + y)
.
G(x)G(y)
In a similar fashion, let λ(x) = ln G(x). That is,
λ(x) = [x]q + ln Γ(q,k) (x + k) − [x]q ln[x]q . Then,
qx
λ(x)0 = ψ(q,k) (x + k) + (ln q)
(ln(1 − q x ) − ln(1 − q)) > 0.
1−q
17
Journal of New Theory 5 (2015) 13-18
Hence G(x) is increasing.
Next, observe that,
[y]
H(x, y) =
G(x + y)
G(x + y) 1
1
[y]q q
=
.
≥
= [y]
G(x)G(y)
G(x) G(y)
G(y)
e q [y]q Γ(q,k) (y)
since G(x) is increasing and Γ(q,k) (y + k) = [y]q Γ(q,k) (y). That implies,
[x]
[y]
Γ(q,k) (x + y + k)
e[x]q +q [y]q
[y]q q
.
≥
H(x, y) =
.
[x+y]q
e[x]q +[y]q Γ(q,k) (x + k)Γ(q,k) (y + k)
e[y]q [y]q Γ(q,k) (y)
[x + y]q
[y]q
x
[x]q q [y]q
establishing the results as in (12).
Γ
(x)Γ
(y)
(q,k)
be the (q, k)-deformation of the classical Beta funcRemark 2.7. Let B(q,k) (x, y) = (q,k)
Γ(q,k) (x+y)
tion. Then, inequality (12) can be written as follows.
[x]q −1 q x [y]q
B(q,k) (x, y) ≤
3
[x]q
e
[x +
Γ(q,k) (y)
.
[x+y]q −1
y]q
Concluding Remarks
Some new inequalities related to (6) and (7) have been established for the q and (q, k) deformed
Gamma functions. In particular, if we allow q → 1 in either inequality (8) or (9), then, inequality
(6) is restored as a special case. Also, by allowing q → 1 in (12), then we obtain the k-analogue of
inequality (11).
Acknowledgement
The authors are very grateful to the anonymous reviewers for their valuable comments which helped
in improving the quality of this paper.
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