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  • دکتری (1377)

    ریاضی محض

    دانشگاه خوارزمی،

  • کارشناسی‌ارشد (1370)

    ریاضی محض

    دانشگاه خوارزمی،

  • کارشناسی (1367)

    ریاضیات کاربردی

    دانشگاه تهران ،

  • آنالیز تابعی
  • جبرهای تابعی
  • جبرهای باناخ

    در سال 1367 کارشناسی ریاضی کاربردی را در دانشگاه تهران به پایان رساندم. در سالهای 1370 و 1377 دوره های ارشد و دکتری را در دانشگاه خوارزمی در گرایش آنالیز تابعی به اتمام رساندم. از سال 1378 عضو هیات علمی دانشگاه تربیت مدرس هستم.

    ارتباط

    رزومه

    Generalized local operators between function modules

    Fereshteh Sady, Masoumeh Najafi Tavani
    Journal PapersMathematical Researches , Volume 7 , Issue 1, 2021 May 10, {Pages 0-0 }

    Abstract

    Let X be a compact Hausdorff space, E be a normed space, A (X, E) be a regular Banach function algebra on X, and A (X, E) be a subspace of C (X, E). In this paper, first we introduce the notion of localness of an additive map S: A (X, E)→ C (X, E) with respect to additive maps T 1,..., T n: A (X)→ C (X) and then we characterize the general form of such maps for a certain class of subspaces A (X, E) of C (X, E) having A (X)-module structure.

    Algebraic reflexivity of diameter-preserving linear bijections between -spaces

    A Jim?nez-Vargas, Fereshteh Sady
    Journal PapersarXiv preprint arXiv:2004.05864 , 2020 April 13, {Pages }

    Abstract

    We prove that if and are first countable compact Hausdorff spaces, then the set of all diameter-preserving linear bijections from to is algebraically reflexive.

    Isometries between completely regular vector-valued function spaces

    Mojtaba Mojahedi, Fereshteh Sady
    Journal PapersarXiv preprint arXiv:2003.01566 , 2020 March 2, {Pages }

    Abstract

    In this paper, first we study surjective isometries (not necessarily linear) between completely regular subspaces and of and where and are locally compact Hausdorff spaces and and are normed spaces, not assumed to be neither strictly convex nor complete. We show that for a class of normed spaces satisfying a new defined property related to their -sets, such an isometry is a (generalized) weighted composition operator up to a translation. Then we apply the result to study surjective isometries between and whenever and are equipped with certain norms rather than the supremum norm. Our results unify and generalize some recent results in this context.

    On 2-local diameter-preserving maps between C (X)-spaces

    A Jim?nez-Vargas, Fereshteh Sady
    Journal PapersarXiv preprint arXiv:2004.06472 , 2020 April 14, {Pages }

    Abstract

    The 2-locality problem of diameter-preserving maps between C (X)-spaces is addressed in this paper. For any compact Hausdorff space X with at least three points, we give an example of a 2-local diameter-preserving map on C (X) which is not linear. However, we show that for first countable compact Hausdorff spaces X and Y, every 2-local diameter-preserving map from C (X) to C (Y) is linear and surjective up to constants in some sense. This yields the 2-algebraic reflexivity of isometries with respect to the diameter norms on the quotient spaces.

    Zero product preserving functionals on C ( Ω ) -valued spaces of functions

    Z Pourghobadi, F Sady, MN Tavani
    Journal Papers , , {Pages }

    Abstract

    Composition in Modulus Maps on Semigroups of Continuous Functions

    Bagher Jafarzadeh, Fereshteh Sady
    Journal PapersarXiv preprint arXiv:1910.09216 , 2019 October 21, {Pages }

    Abstract

    For locally compact Hausdorff spaces and , and function algebras and on and , respectively, surjections satisfying norm multiplicative condition , , with respect to the supremum norms, and those satisfying have been extensively studied. Motivated by this, we consider certain (multiplicative or additive) subsemigroups and of and , respectively, and study surjections satisfying the norm condition , , for some class of two variable positive functions . It is shown that is also a composition in modulus map.

    Additive jointly separating maps and ring homomorphisms

    Fereshteh Sady, Masoumeh Najafi Tavani
    Journal PapersarXiv preprint arXiv:1907.10286 , 2019 July 24, {Pages }

    Abstract

    Let and be compact Hausdorff spaces, and be real or complex normed spaces and be a subspace of . For a function , let $\coz (f) $ be the cozero set of . A pair of additive maps $ S, T: A (X, E)\lo C (Y, F) $ is said to be jointly separating if $\coz (Tf)\cap\coz (Sg)=\emptyset $ whenever $\coz (f)\cap\coz (g)=\emptyset $. In this paper, first we give a partial description of additive jointly separating maps between certain spaces of vector-valued continuous functions (including spaces of vector-valued Lipschitz functions, absolutely continuous functions and continuously differentiable functions). Then we apply the results to characterize continuous ring homomorphisms between certain Banach algebras of vector-valued continuous functions

    Lattice isomorphisms between certain sublattices of continuous functions

    Vahid Ehsani, Fereshteh Sady
    Journal PapersarXiv preprint arXiv:1907.08786 , 2019 July 20, {Pages }

    Abstract

    Let be the lattice of all continuous functions on a compact Hausdorff space with values in the unit interval . We show that for compact Hausdorff spaces and and (not necessarily contain constants) sublattices and of and , respectively, which satisfy a certain separation property, any lattice isomorphism induces a homeomorphism . If, furthermore, and are closed under the multiplication, then has a representation , , for all points in a dense subset of , where each is a strictly increasing continuous bijection on . In particular, for the case where and are metric spaces and and are the lattices of all Lipschitz functions with values in , the set is the whole of .

    Generalized norm preserving maps between subsets of continuous functions

    Bagher Jafarzadeh, Fereshteh Sady
    Journal PapersPositivity , Volume 23 , Issue 1, 2019 February 5, {Pages 111-123 }

    Abstract

    Let X and Y be locally compact Hausdorff spaces. In this paper we study surjections between certain subsets A and B of and , respectively, satisfying the norm condition , , for some continuous function . Here and denote the supremum norms on and , respectively. We show that if A and B are (positive parts of) subspaces or multiplicative subsets, then T is a composition operator (in modulus) inducing a homeomorphism between strong boundary points of A and B. Our results generalize the recent results concerning multiplicatively norm preserving maps, as well as, norm additive in modulus maps between function algebras to more general cases.

    Zero product preserving functionals on -valued spaces of functions

    Ziba Pourghobadi, Fereshteh Sady, Masoumeh Najafi Tavani
    Journal PapersAnnals of Functional Analysis , 2019 January , {Pages 14-Jan }

    Abstract

    Let X be a compact Hausdorff space and be a locally compact -compact space. In this paper we study (real-linear) continuous zero product preserving functionals on certain subalgebras A of the Fr?chet algebra . The case that is continuous with respect to a specified complete metric on A will also be discussed. In particular, for a compact Hausdorff space K we characterize -continuous linear zero product preserving functionals on the Banach algebra equipped with the norm , where denotes the supremum norm. An application of the results is given for continuous ring homomorphisms on such subalgebras.

    A note on nonlinear isometries between vector-valued function spaces

    Arya Jamshidi, Fereshteh Sady
    Journal PapersLinear and Multilinear Algebra , 2018 July 28, {Pages 11-Jan }

    Abstract

    Let X and Y be compact Hausdorff spaces, E and F be Banach spaces over or and let A and B be subspaces of and, respectively. In this paper, we investigate the general form of isometries (not necessarily linear) T from A onto B. If F is strictly convex, then there exist a subset of Y, a continuous function onto the set of strong boundary points of A and a family of real-linear operators from E to F with such that In particular, we get some generalizations of the vector-valued Banach–Stone theorem and a generalization of a result of Cambern. We also give a similar result when F lacks the strict convexity and its unit sphere contains a singleton as a maximal convex subset.

    Completely square-zero preserving maps on

    Mohammad B Asadi, Hossein Khodaiemehr, Fereshteh Sady
    Journal PapersLinear and Multilinear Algebra , Volume 66 , Issue 5, 2018 May 4, {Pages 937-941 }

    Abstract

    Let be a complex Hilbert space with and be a surjective map on the real linear space of all bounded self-adjoint operators on. For each, let be defined by In this paper, we show that if preserves square-zero operators in both directions, then there exist and a unitary or an antiunitary operator U on such that, for all. We also give a description of all continuous surjective maps, such that preserves square-zero operators in both directions.

    Isometries on certain non-complete vector-valued function spaces

    Mojtaba Mojahedi, Fereshteh Sady
    Journal PapersarXiv preprint arXiv:1809.00328 , 2018 September 2, {Pages }

    Abstract

    In the recent paper\cite {Hos}, surjective isometries, not necessarily linear, between vector-valued absolutely continuous functions on compact subsets and of the real line, has been described. The target spaces and are strictly convex normed spaces. In this paper, we assume that and are compact Hausdorff spaces and and are normed spaces, which are not assumed to be strictly convex. We describe (with a short proof) surjective isometries between certain normed subspaces and of and , respectively. We consider three cases for with some mild conditions. The first case, in particular, provides a short proof for the above result, without assuming that the target spaces are strictly convex. The other cases give some generalizations i

    Jointly separating maps between vector-valued function spaces

    Z Pourghobadi, M Najafi Tavani, F Sady
    Journal PapersarXiv preprint arXiv:1804.10915 , 2018 April 29, {Pages }

    Abstract

    Let and be compact Hausdorff spaces, and be real or complex Banach spaces, and be a subspace of . In this paper we study linear operators $ S, T: A (X, E)\lo C (Y, F) $ which are jointly separating, in the sense that $\coz (f)\cap\coz (g)=\emptyset $ implies that $\coz (Tf)\cap\coz (Sg)=\emptyset $. Here $\coz (\cdot) $ denotes the cozero set of a function. We characterize the general form of such maps between certain class of vector-valued (as well as scalar-valued) spaces of continuous functions including spaces of vector-valued Lipschitz functions, absolutely continuous functions and continuously differentiable functions. The results can be applied for a pair $ T: A (X)\lo A (X) $ and $ S: A (X, E)\lo A (X, E) $ of linear operators,

    A characterization of nonlinear H?lder seminorm preserving bijections

    Arya Jamshidi, Fereshteh Sady, Azin Golbaharan
    Journal PapersPositivity , Volume 22 , Issue 1, 2018 March 1, {Pages 16-Jan }

    Abstract

    For a compact metric space (X, d) and α ∈ (0, 1) α∈(0, 1), let Lip^ α (X) Lip α (X) be the linear space of all complex-valued functions f on X satisfying and lip^ α (X) lip α (X) be the subspace of Lip^ α (X) Lip α (X) consisting of functions f with\lim f (x)-f (y) d^ α (x, y)= 0 lim f (x)-f (y) d α (x, y)= 0 as d (x, y) → 0 d (x, y)→ 0. In this paper, we give a characterization of a bijective map T: lip^ α (X) ⟶ lip^ α (Y) T: lip α (X)⟶ lip α (Y), not necessarily linear, which is an isometry with respect to the H?lder seminorm L (⋅) L (?). It is shown that there exist K_0> 0 K 0> 0, a surjective map Ψ: Y ⟶ X Ψ: Y⟶ X with d^ α (y, z)= K_0\, d^ α (Ψ (y), Ψ (z)) d α (y, z)= K 0 d α (Ψ (y), Ψ (z)) for

    Function Spaces and Nonsymmetric Norm Preserving Maps

    Hadis Pazandeh, Fereshteh Sady
    Journal PapersBulletin of the Belgian Mathematical Society-Simon Stevin , Volume 25 , Issue 5, 2018 January , {Pages 729-740 }

    Abstract

    Let be compact Hausdorff spaces and be either closed subspaces of and , respectively, containing constants or positive cones of such subspaces. In this paper we study surjections satisfying the norm condition for all , where and denote the supremum norms. We show that under a mild condition on the strong boundary points of and (and the assumption in the subspace case), the map is a weighted composition operator on the set of strong boundary points of . This result is an improvement of the known results for uniform algebra case to closed linear subspaces and their positive cones.

    A characterization of nonlinear Hölder seminorm preserving bijections

    A Jamshidi, F Sady, A Golbaharan
    Journal Papers , , {Pages }

    Abstract

    Norm conditions on maps between certain subspaces of continuous functions

    Razieh Sadat Ghodrat, SADY Fereshteh, Arya Jamshidi
    Journal PapersTokyo Journal of Mathematics , Volume 40 , Issue 2, 2017 January , {Pages 421-437 }

    Abstract

    For a locally compact Hausdorff space , let be the Banach space of continuous complex-valued functions on vanishing at infinity endowed with the supremum norm . We show that for locally compact Hausdorff spaces and and certain (not necessarily closed) subspaces and of and , respectively, if is a surjective map satisfying one of the norm conditions i) , or ii) ,\noindent for some and all , then there exists a homeomorphism between the Choquet boundaries of and such that for all and . We also give a result for the case where is closed (or, in general, satisfies a special property called Bishop's property) and is a surjective map satisfying the inclusion of peripheral ranges. As an application, we characterize such maps betwee

    Maps Preserving 2-Idempotency of Certain Products of Operators

    Hossein Khodaiemehr, Fereshteh Sady
    Journal PapersFilomat , Volume 31 , Issue 12, 2017 September 15, {Pages }

    Abstract

    Let A, B be standard operator algebras on complex Banach spaces X and Y of dimensions at least 3, respectively. In this paper we give the general form of a surjective (not assumed to be linear or unital) map Φ: A−→ B such that Φ2: M2 (C)⊗ A→ M2 (C)⊗ B defined by Φ2 ((sij) 2? 2)=(Φ (sij)) 2? 2 preserves nonzero idempotency of Jordan product of two operators in both directions. We also consider another specific kinds of products of operators, including usual product, Jordan semi-triple product and Jordan triple product. In either of these cases it turns out that Φ is a scalar multiple of either an isomorphism or a conjugate isomorphism.

    Point multipliers and the Gleason–Kahane–Żelazko theorem

    Razieh Sadat Ghodrat, Fereshteh Sady
    Journal PapersBanach Journal of Mathematical Analysis , Volume 11 , Issue 4, 2017 January , {Pages 864-879 }

    Abstract

    Let A be a Banach algebra, and let X be a left Banach A-module. In this paper, using the notation of point multipliers on left Banach modules, we introduce a certain type of spectrum for the elements of X and we also introduce a certain subset of X which behaves as the set of invertible elements of a commutative unital Banach algebra. Among other things, we use these sets to give some Gleason–Kahane–Żelazko theorems for left Banach A-modules.

    دروس نیمسال جاری

    • دكتري
      جبرهاي تابعي ( واحد)
      دانشکده علوم ریاضی، گروه رياضي محض
    • كارشناسي ارشد
      آناليز حقيقي 2 ( واحد)

    دروس نیمسال قبل

    • دكتري
      مباحثي در آناليز تابعي ( واحد)
      دانشکده علوم ریاضی، گروه رياضي محض
    • حسین, خدائی مهر
    • 1393
      احساني, وحيد
      نگاشت هاي ترتيب و ضربي بين مشبكه ها و نيم گروه هايي از توابع پيوسته
    • رییس بخش ریاضی
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