
1. Introduction
A decisive break in the theory of matrix transformations was in 1950, when Robinson considered the action of infinite matrices of linear operators from a Banach space on sequences of elements of that space [1]. In the past years, many remarkable results [2] [3] [4] were yielded in this direction.
Let X and Y be topological vector spaces, and
. For sequence families
and
, the matrix
means that
converges when
,
and
for each
.
As usual,
In 2001, Li Ronglu depicted the nonlinear operator matrices transformation with some restrictive condition on topological vector spaces [5]. In the next year, Li Ronglu gave some clear-cut characterizations of the matrix families
and
consisted of matrices of linear and some nonlinear operators between topological vector spaces [6]. In this paper, we study the summability theory for a class of matrices of nonlinear mapping on Banach space, and discuss the characterization of the matrix classes:
,
,
.
All of the researches enrich the results on infinite matrices transformations, and have important meaning for the study of Banach space.
2. Preliminaries and Lemmas
In 1993, nonlinear Schur Theorem was given by Li Ronglu and C. Swartz, and broke the limitations of linear operator matrices.
Theorem A. [7] Let G be an Abelian topological group,
,
a matrix in
such that
for some
and all
. If
i.e.,
exists for each
, then the series
converges uniformly with respect to both
and
, and
exists for every
. If, in addition, G is sequentially complete, then the converse implication is true.
As a special case, the following theorem is a nice result for the matrix family
.
Theorem B. [8] Let
be topological vector spaces and
a mapping such that
for every
. If
, then for every bounded
, the series
converges uniformly with respect to both
and
and
exists for every
. If, in addition, Y is sequentially complete, then the converse implication is true.
Note that theorem B exceeded the restriction of linear operators, and a characterization of
was given. For Banach spaces
, it is useful to discuss the characterization of a variety of matrix families, where the mapping need not be linear.
As preparation of the proves of the main results, we also need following lemma.
Lemma [9]
if and only if
for all
.
3. Main Results
Unless otherwise noted
below are Banach spaces, and the mapping we studied in this section need not be linear.
Theorem 1. Let
for all
, then
if and only if
(i)
exists for all
and
;
(ii) For any
,
there exists
such that
for all natural number
,
, and
with
.
Proof. Necessity of condition (i) and (ii) is easy to prove by the theorem B in Introduction.
Now suppose that (i) and (ii) are hold, and
, then for any
, there exists
such that
for all
by the condition (ii). And because of condition (i) there is
, such that
for all
. Hence we have
(1)
for all
. Therefore
So
is a Cauchy sequence in Y. Therefore
converges by the completeness of Y, and then
. The sufficiency is proved. Q.E.D.
Since
, we can get the next corollary by the theorem.
Corollary 1. Suppose that
, then
if and only if
for all
, and for any
, there exists
such that
for all
, and
with
.
Proof. Necessity is clear by above theorem and the definition of
.
Conversely, let
, then for any
, there exists
such that
for all
. Since
for all
and
, there is
, such that
for all
and
.
Hence we have
. (2)
So column
converges to 0, and then
. The sufficiency is proved. Q.E.D.
Theorem 2. Let
with respect to
, then
if and only if
(i)
for all
;
(ii) For any
and
, there exists
such that
for all
and
with
.
Proof. ⇒) Suppose that
, the condition (i) is clear.
Since
for every
,
for every
by lemma 1, that is
. Hence, for every
, we have
. Therefore, by above corollary, for every
and
there is
such that for all
,
, and
, we have
. (3)
condition (ii) is proved.
⇐) For every
, and
, we have
by the condition (i). Because of the condition (ii), we have
by the Corollary 1, and then for
, we have
is hold for every
. Therefore
by lemma 1, and then
. Q.E.D.
Theorem 3. Let
with respect to
, then
if and only if
(i)
for all
and
;
(ii) For any
and
, there exists
such that
(4)
Proof. For
, since
,
for any
and
, by condition (i). So condition (i) and (ii) is equivalent to
by corollary 1.
Suppose that
, then
for all
. By lemma 1,
, for all
and
. Hence
.
On the other hand, suppose that
. For every
, there exists
and
, such that
, and so
. Hence
. Q.E.D.
Theorem 4. Let
with respect to
, then
if and only if
(i)
for all
and
;
(ii) For any
and
, there exists
, such that
for all
and
.
Proof. By condition (i), for all
and
,
. (5)
By theorem 2, condition (i) and (ii) are equivalent to
. Next, we prove that
for all
is equivalent to
.
In fact, If
, and let
, then
. Since
for all
by lemma, we have
. So
. On the other hand, suppose that
. Since for any
, there must be
,
, such that
, we have
, (6)
and then
. Q.E.D.
4. Result
In this paper, we first review the research history of infinite matrix transformation, and then we mainly study the summability of a class of nonlinear mapping matrices in Banach space.
And some new results about, matrix transformation theorems are obtained: we characterize the matrix classes such as
,
,
,
.
Acknowledgements
This research was supported by the Science and Technology Project of Jilin Provincial Department of Education (JJKH20180891KJ).
NOTES
*Corresponding author.