# Search results for: Janusz BRZDĘK

Journal of Fixed Point Theory and Applications > 2018 > 20 > 4 > 1-16

Aequationes mathematicae > 2018 > 92 > 5 > 975-991

Journal of Fixed Point Theory and Applications > 2018 > 20 > 2 > 1-10

*X*be a complex linear space, endowed with an extended (that is, admitting infinite values) norm. We prove a fixed point theorem for operators of the form $$p_3 \mathcal {L}^3 + p_2 \mathcal {L}^2 +p_1\mathcal {L}$$ p3L3+p2L2+p1L , where $$ \mathcal {L}:X\rightarrow X$$ L:X→X is linear and $$p_1,p_2,p_3$$ p1,p2,p3 are fixed scalars. That result has been motivated by some issues arising in Ulam...

Acta Mathematica Scientia > 2018 > 38 > 2 > 377-390

Aequationes mathematicae > 2018 > 92 > 2 > 355-373

Acta Mathematica Scientia > 2017 > 37 > 6 > 1727-1739

Journal of Mathematical Analysis and Applications > 2017 > 453 > 1 > 620-628

Journal of Fixed Point Theory and Applications > 2017 > 19 > 4 > 2441-2448

Aequationes mathematicae > 2017 > 91 > 3 > 445-477

Journal of Mathematical Analysis and Applications > 2016 > 442 > 2 > 537-553

Applied Mathematics Letters > 2016 > 54 > C > 31-35

Applied Mathematics and Computation > 2016 > 276 > C > 158-171

^{*}-algebras. The main tool in the proofs...

Aequationes mathematicae > 2016 > 90 > 4 > 671-681

Journal of Fixed Point Theory and Applications > 2015 > 17 > 4 > 659-668

Aequationes mathematicae > 2015 > 89 > 1 > 83-96

Aequationes mathematicae > 2014 > 88 > 1-2 > 169-173

*A*be a subgroup of a commutative group (

*G*, +) and

*P*be a quadratically closed field. We give the full description of all pairs of functions

*f*:

*G*→

*P*and

*g*:

*A*→

*P*such that

*f*(

*x*+

*y*) +

*f*(

*x*−

*y*) = 2

*f*(

*x*)

*g*(

*y*) for (

*x*,

*y*) ∈

*G*×

*A*.

Aequationes mathematicae > 2014 > 87 > 3 > 379-389

*X*be a normed space over $${\mathbb{K}, \mathcal{F} : = \{f \in X^I : {\rm lim}_{t \to \infty} f(t) {\rm exists} \, {\rm in} X\},\hat{a} \in \mathbb{K}, \mathcal{A}(\hat{a}) : = \{\alpha \in \mathbb{K}^I : {\rm lim}_{t \to \infty} \alpha(t) = \hat{a}\},}$$ and ...

Fixed Point Theory and Applications > 2013 > 2013 > 1 > 1-9

**MSC:**39B82, 47H10.

Aequationes mathematicae > 2013 > 85 > 1-2 > 169-183

*A*be a subgroup of a commutative group (

*G*, + ) and

*P*be a commutative ring. We give the full description of functions $${g: G \rightarrow P}$$ satisfying $$g(x + y) + g(x - y) = 2g(x)g(y) \quad (x, y) \in A \times G. \quad\quad\quad\quad (A)$$ Thus we obtain a family of functions depicting evolutions of quite arbitrary functions $${g_0 : G \to P}$$ into cosine functions $${g:...

Advances in Difference Equations > 2013 > 2013 > 1 > 1-12

**MSC:**39B82, 47H10.