1. Introduction
Let
and
be a normed spaces on the same field
, and
. We use the notation
for all the norm on both
and
. In this paper, I study and expand the
-function equation from non-Archimedean normed space to non-Archimedean random normed space.
In fact, when
is non-Archimedean normed space and
is non-Archimedean Banach spaces.
Or
is a vector over field
and
be a non-Archimedean random Banach space over field
. We solve and prove the Hyers-Ulam-Rassisa type stability of forllowing quadratic λ-functional equation.
(1)
where: Let
, λ is a fixed non-Archimedean number with
and
is a positive integer. The notions of non-Archimedean normed space and non-Archimedean Banach spaces and non-Archimedean random Banach space over field
will remind in the next section. The study the stability of generalized stability of the quadratic type λ-functional equation with variables in non-Archimedean Banach space and non-Archimedean Random normed space originated from a question of S.M. Ulam [1] , concerning the stability of group homomorphisms. Let
be a group and let
be a metric group with metric
. Geven
, does there exist a
such that if
satisfies
then there is a homomorphism
with
The Hyers [2] gave firts affirmative partial answer to the equation of Ulam in Banach spaces. After that, Hyers’ Theorem was generalized by Aoki [3] additive mappings and by Rassias [4] for linear mappings considering an unbouned Cauchy difference. Gajda following the same approach as in Rassias gave an affirmative solution to this question for
. It was shown by Gajda [5] , as well as by Rassias and Semr [6] that one cannot prove a Rassias, type theorem when
. The counterexamples of Gajda, as well as of Rassias and Semr have stimulated several matematicians to invent new definition of approximately additive or approximately linear mappings, was obtained by Găvruta [7] .
The functional equation
is called the Cauchy equation. In particular, every solution of the Cauchy equation is said to be an additive mapping.
The functonal equation
is called the quadratic functional equation. In particular, every solution of the quadratic functional equation is said to be a quadratic functional mapping.
The stability the quadratic functional equation was proved by Skof [8] for mappings
, where
is a normed space and
is a Banach space.
Recently the author studied the Hyers-Ulam stability for the following α-functional equation.
in Non-Archimedean Banach spaces and non-Archimedean Random normed space.
In this paper, we solve and proved the Hyers-Ulam stability for λ-functional Equation (1.1), i.e. the λ-functional equation with 3k-variables. Under suitable assumptions on spaces
and
, we will prove that the mappings satisfying the λ-functional Equation (1.1). Thus, the results in this paper are generalization of those in [9] for λ-functional equation with 3k-variables.
In this paper, based on the work of world mathematicians [1] - [33] , I introduce a new generalized quadratic function equation with 3k-variables to improve the classical form, which is a new breakthrough for the development of this field functional equation.
The paper is organized as followns: In section preliminarier we remind some basic notations in [10] [11] [12] [13] [14] such as non-Archimedean field, Non-Archimedean normed space and non-Archimedean Banach space, Random normed spaces, Non-Archimedean random normed space.
Section 3: Establishing the solution for (1.1) by the fixed point method in Non-Archimedean Banach space.
+ Condition for existence of solutions for Equation (1.1)
+ Constructing a solution for (1.1).
Section 4: Establishing the solution for (1.1) by the direct method in Non-Archimedean Banach space
Section 5: Construct a solution for (1.1) on non-Archimedean Random normed space.
2. Preliminaries
2.1. Non-Archimedean Normed and Banach Spaces
A valuation is a function
from a field
into
such that 0 is the unique element having the 0 valuation,
and the triangle inequality holds, i.e.;
A field
is called a valued filed if
carries a valuation. The usual absolute values of
and
are examples of valuation. Let us consider a vavluation which satisfies a stronger condition than the triangle inaquality. If the tri triangle inequality is replaced by
then the function
is called a norm-Archimedean valuational, and filed. Clearly
and
. A trivial example of a non-Archimedean valuation is the function
talking everything except for 0 into 1 and
this paper, we assume that the base field is a non-Archimedean filed, hence call it simply a filed. Let be a vecter space over a filed
with a non-Archimedean
. A function
is said a non-Archimedean norm if it satisfies the follwing conditions:
1)
if and only if
;
2)
;
3) the strong triangle inequlity
hold. Then
is called a norm-Archimedean norm space.
1) Let
be a sequence in a non-Archimedean normed space X. Then sequence
is called cauchy if for a given
there a positive integer N such that
for all
2) Let
be a sequence in a norm-Archimedean normed space X. Then sequence
is called cauchy if for a given
there a positive integer N such that
for all
. The we call
a limit of sequence
and denote
.
3) If every sequence Cauchy in X converger, then the norm-Archimedean normed space X is called a norm-Archimedean Bnanch space.
2.2. Random Normed Spaces
A random normed space is triple
, where
is a vector space, T is a is a continuous t-norm, and
is a mapping from
into
such that, the following conditions hold:
1) (RN1)
for all
if and only if
;
2) (RN2)
for all
,
;
3) (RN3)
for all
,
;
Note: If
is a random normed space an
is a sequence such that
then
almost everywhere.
2.3. Non-Archimedean Random Normed Space
A non-Archimedean random normed space is triple
, where
is a linear space over a non-Archimedean filed
, T is a is a continuous t-norm, and
is a mapping from
into
such that, the following conditions hold:
1) (NA-RN1)
for all
if and only if
;
2) (NA-RN2)
for all
,
,
;
3) (NA-RN3)
for all
,
;
It is easy to see that if (NA-RN3) hold then so is (RN3)
Let
is a non-Archimedean random normed space. Suppose
is a sequence in
. Then
is said to be convergent if there exists
such that
for all
. In that case, x is called the limit of sequence
Theorem 1. Let
be a complete generalized metric space and let
be a strictly contractive mapping with Lipschitz constant
. Then for each given element
, either
for all nonegative integers n or there exists a positive integer
such that
1)
,
;
2) The sequence
converges to a fixed point
of J;
3)
is the unique fixed point of J in the set
;
4)
2.4. Solutions of the Equation
The functional equation
is called the cauchuy equation. In particular, every solution of the cauchuy equation is said to be an additive mapping.
The functional equation
is called the quadratic functional equation In particular, every solution of the quadratic functional equation is said to be an quadratic mapping.
The functional equation
is called a Jensen type the quadratic functional equation
3. Establishing the of (1.1) in Non-Archimedean Banach Space
3.1. Condition for Existence of Solutions for Equation (1.1)
Note that for Quadratic λ-functional equation,
and
is be vector space.
Lemma 2. Suppose
and
be vector space. If mapping
satisfying
(2)
for all
for all
then
is quadratic type
Proof. Assume that
satisfies (2)
We replacing
by
in (2), we get
(3)
So
.
Next we replacing
by
in (2), we have
(4)
and so
for all
. Thus from (2)
(5)
for all
for all
Next now we replacing
by
in (2), we have
(6)
for all
.
Next we replace x by 2x, we get
(7)
for all
. for all
, So from (6) and (7) we have the general case for every m being a positive integer, we have
(8)
for all
, So we get the desired result.
Notice now we replacing
by
in (5) we have
So, the function f is quadratic. □
3.2. Constructing a Solution for (1.1)
Now, we first study the solutions of (1.1). Note that for Quadratic λ-functional equation,
is a non-Archimedean normed space and
is a non-Archimedean Banach spacebe then use fixed point method, we prove the Hyers-Ulam stability of the Quadratic λ-functional equation in Non-Archimedean Banach space. Under this setting, we can show that the mapping satisfying (1.1) is quadratic. These results are give in the following.
Theorem 3. Suppose
be a function such that there exists an
with
(9)
for all
, for all
. Let
be a mapping satisfying
and
(10)
for all
, for all
. Then there exists a unique quadratic type mapping
such that
(11)
for all
.
Proof. We replacing
by
in (10), we get
(12)
for all
for all
.
Now we consider the set
and introduce the generalized metric on S as follows:
where, as usual,
. That has been proven by mathematicians
is complete see [14]
Now we cosider the linear mapping
such that
for all
. Let
be given such that
then
for all
.
Hence
for all
. So
implies that
. This means that
for all
. It folows from (12) that
for all
. So
for all
By Theorem 1.2, there exists a mapping
satisfying the fllowing:
1) H is a fixed point of T, i.e.,
(13)
for all
. The mapping H is a unique fixed point T in the set
This implies that H is a unique mapping satisfying (13) such that there exists a
satisfying
for all
2)
as
. This implies equality
for all
3)
. Which implies
for all
. It follows (9) and (10) that
for all
for all
. So
for all
for all
. By Lemma 3.1, the mapping
is quadratic type. □
Theorem 4. Suppose
be a function such that there exists an
with
(14)
for all
, for all
. Let
be a mapping satisfying
and
(15)
for all
, for all
. Then there exists a unique quadratic type mapping
such that
(16)
for all
.
The rest of the proof is similar to the proof of theorem 3.2 with note that mapping
,
.
Corollary 1. Let
and
be nonegative real numbers and let
be a mapping satisfying
and
(17)
for all
. Then there exists a unique quadratic type mapping
such that
(18)
for all
.
Corollary 2. Let
and
be nonegative real numbers and let
be a mapping satisfying
and
(19)
for all
. Then there exists a unique quadratic type mapping
such that
(20)
for all
.
4. Establishing a Solution to the Quadratic λ-Functional Equation Using the Direct Methoduse in Non-Archimedean Banach Space
Next, we are going to study the solutions of (1.1) for Quadratic λ-functional equation use direct method, we prove the Hyers-Ulam stability of the Quadratic λ-functional equation, the
is a Non-Archimedean normed space and
is a Non-Archimedean Banach space, and the field
satisfy
. Under this setting, we can show that the mapping satisfying (1.1) is quadratic. These results are give in the following
Theorem 5. Let
be a function and let
be a mapping satisfying
and
(21)
(22)
for all
for all
. Then there exists a unique quadratic type mapping
such that
(23)
for all
.
Proof. We replacing
by
in (22), we have
(24)
for all
. Therefore
(25)
for all
.
Hence
(26)
for all nonnegative integers m and l with
and all
. It follows (26)
that the sequence
is a Cauchy sequence for all
. Since
is complete, the sequence
converger so one can define the mapping
by
for all
. Moreover, letting
and passing the limit
in (26), we get (23). It follows from (21) and (22) that
(27)
for all
.
for all
. By Lemma 3.1, the mapping
is quadratic. Now, let
be another quadratic mapping satisfying (23). Then we have
which tends to zero as
for all
. So we can conclude that
for all
. This proves the uniqueness of H. Thus the mapping
is a unique quadratic mapping satisfying (23) □
Theorem 6. Let
be a function and let
be a mapping satisfying
and
(28)
(29)
for all
for all
. Then there exists a unique quadratic type mapping
such that
(30)
for all
.
The rest of the proof is similar to the proof of theorem 4.1.
Corollary 3. Let
and
be nonegative real numbers and let
be a mapping satisfying
and
(31)
for all
. Then there exists a unique quadratic mapping
such that
for all
.
Corollary 4. Let
, and
be nonegative real numbers and let
be a mapping satisfying
and
(32)
for all
. Then there exists a unique quadratic mapping
such that
for all
.
5. Construct a Solution for (1.1) on Non-Archimedean Random Normed Space
In this section,
be a non-Archimedean field,
is a vector space over
and let
be a non-Archimedean random Banach space over
We investigate the stability of the quadratic functional equation
(33)
where
and
.
Next, we define a random approximately quadrtic function. Let
be a distribution function such that
is symmetric, nondecreasing and
(34)
For
,
.
Next, we define:
A mapping
is said to be φ-approximately quadratic mapping if
(35)
for all
, for all
,
.
* Note: We assume that
in
Theorem 7 For
be a φ-approximately quadratic mapping if there exist an
and an integer h,
with
and
such that
(36)
for all
for all
,
and
(37)
for all
and
.
Then there exists a unique quadratic type mapping
such that
(38)
In there
(39)
for all
and
.
Proof. First, we show by induction on j that for each
,
and
,
(40)
we replacing
by
in (35), we obtain
(41)
,
. This proves (40) for
. We now assume that (40) holds for some
Next we replacing
by
in (35) we have
(42)
Since
(43)
for all
. So in (40) holds for all
.
Other way
(44)
Next we replacing x by
in (44) and using inequality (36), we have
(45)
Then
(46)
Hence,
(47)
Since
is a Cauchy sequence in the non-Archimedean random Banach space
. Hence, we can define a mapping
such that
(48)
Next for each
,
and
.
(49)
Therefore,
(50)
By letting
, we obtain
(51)
As T is continuous, from a well-known result in probabilistic metric space see [12] .
Now we put
(52)
it follows that
(53)
for almost all
, □
On the other hand, replacing
by
, respectively, in (35) and suing (NA-RN2) and (36), we have
(54)
for all
. Sence
We infer that Q is a quadratic function.
Finally we have to prove that Q is a unique quadratic mapping.
Let
is another quadratic mapping such that
(55)
for all
and
, then for each
(56)
Form (48), we infer that
.
From the theorem 5.1 we get the following corollary:
Corollary 5. For
be a φ-approximately quadratic mapping if there exist an
and an integer
with
and
such that
(57)
for all
for all
,
, then there exists a unique quadratic type mapping
such that
(58)
for all
and
. In there
(59)
for all
and
.
Application Example: For
non-Archimedean random normed space in which
and assuming that
complete non-Archimedean random normed space.
Now we define
It is easy to see that for
then (36) holds, sence
We have
,
,
.
6. Conclusion
In this paper, I have built the condition for existence of a solution for a functional equation of general form and then I have used two fixed point methods and a direct method to show their solutions on non-Archimedean space and finally establish their solution on the non-Archimedean Random normed space.