doktorska disertacija
Nina Peršin (Author), Joso Vukman (Mentor), Maja Fošner (Co-mentor)

Abstract

V doktorski disertaciji so obravnavane funkcionalne enačbe, ki so v zvezi z odvajanji, centralizatorji in sorodnimi preslikavami na prakolobarjih. Med slovenskimi matematiki se je s tem področjem matematike v osemdesetih letih prejšnjega stoletja začel prvi ukvarjati J. Vukman, sledili so M. Brešar, B. Zalar, B. Hvala in v novejšem času M. Fošner, D. Benkovič, D. Eremita, I. Kosi-Ulbl in A. Fošner. Osnovno sredstvo pri reševanju tovrstnih funkcionalnih enačb je uporaba teorije funkcijskih identitet. Nekoliko natančneje pojasnimo omenjene pojme. Aditivna preslikava ▫$D$▫, ki slika poljuben kolobar ▫$R$▫ vase, je odvajanje, če velja ▫$D(xy) = D(x)y + xD(y)$▫ za vsak par ▫$x, y$▫ iz ▫$R$▫ in je jordansko odvajanje, če velja ▫$D(x^2)=D(x)x +xD(x)$▫. Očitno je, da je vsako odvajanje tudi jordansko odvajanje, obratno pa v splošnem ne velja. I. N. Herstein je leta 1957 dokazal, da je vsako jordansko odvajanje na prakolobarju s karakteristiko različno od dva, odvajanje. V doktorski disertaciji se najprej osredotočimo na funkcionalne enačbe, ki so v zvezi z odvajanji. Obravnavali smo funkcionalni enačbi ▫$D(x^3=D(x^2)x + x^2D(x)$▫ in ▫$D(x^3)=D(x)x^2+ xD(x^2)$▫, kjer je ▫$D$▫ aditivna preslikava, ki slika prakolobar s primernimi omejitvami glede karakteristike vase. Dokazali smo, da je ▫$D$▫ odvajanje. Nadalje poiščemo tudi rešitev funkcionalne enačbe ▫$2D(x^{m+n+1})=(m+n+1)(x^mD(x)x^n+x^nD(x)x^m)$▫, kjer sta ▫$m \ge 1$▫ in ▫$n \ge 1$▫ fiksni naravni števili in ▫$D$▫ neničelna aditivna preslikava, ki slika prakolobar s primernimi omejitvami glede karakteristike vase. Dokažemo, da je ▫$D$▫ odvajanje in ▫$R$▫ komutativen kolobar. V tretjem poglavju so obravnavane funkcionalne enačbe, ki so v zvezi s centralizatorji. Aditivna preslikava ▫$T$▫, ki slika poljuben kolobar ▫$R$▫ vase, je levi (desni) centralizator, če je ▫$T(xy)=T(x)y (T(xy)=xT(y))$▫ za vsak par ▫$x, y$▫ iz ▫$R$▫. V prvem podpoglavju tega razdelka je obravnavana funkcionalna enačba ▫$2T(x^{m+n+1})=x^mT(x)x^n +x^nT(x)x^m$▫ na prakolobarju s primernimi omejitvami glede karakteristike, kjer sta ▫$m \ge 0$▫ in ▫$n \ge 0$▫ fiksni celi števili in ▫$m+n$▫ je različno od ▫$0$▫. Dokažemo, da je ▫$T$▫ dvostranski centralizator. Aditivna preslikava ▫$T$▫, ki slika poljuben kolobar ▫$R$▫ vase, je ▫$(m,n)$▫-jordanski centralizator, če je ▫$(m+n)T(x^2)=mT(x)x+nxT(x)$▫ za vsak ▫$x$▫ iz ▫$R$▫, kjer sta ▫$m$▫ in ▫$n$▫ fiksni nenegativni celi števili in ▫$m+n$▫ je različno od ▫$0$▫. Ta pojem je leta 2010 vpeljal J. Vukman ter med drugim tudi dokazal, da vsak ▫$(m,n)$▫-jordanski centralizator na poljubnem kolobarju ▫$R$▫ zadošča pogoju ▫$2(m+n)^2T(xyx) = mnT(x)xy + m(2m + n)T(x)yx -mnT(y)x^2 + 2mnxT(y)x - mnx^2T(y) + n(m + 2n)xyT(x) + mnyxT(x)$▫ za vsak par ▫$x, y$▫ iz ▫$R$▫. Če v tej identiteti pišemo ▫$y = x$▫, dobimo naslednjo funkcionalno enačbo ▫$2(m+n)^2T(x3)=m(2m+n)T(x)x^2+2mnxT(x)x+n(m+2n)x^2T(x)$▫, ki je obravnavana v zadnjem delu doktorske disertacije na prakolobarju s primernimi omejitvami glede karakteristike, kjer sta ▫$m$▫ in ▫$n$▫ fiksni naravni števili. Dokažemo, da je ▫$T$▫ dvostranski centralizator. V zaključnem poglavju podamo odprta vprašanja o funkcionalnih enačbah, ki so v zvezi s posplošenimi odvajanji in ▫$(\theta, \phi)$▫- odvajanji, kjer sta ▫$\theta$▫ in ▫$\phi$▫ avtomorfzma na kolobarju ▫$R$▫.

Keywords

funkcionalne enačbe;odvajanje;centralizator;preslikave;prakolobarji;disertacije;

Data

Language: Slovenian
Year of publishing:
Typology: 2.08 - Doctoral Dissertation
Organization: UM FNM - Faculty of Natural Sciences and Mathematics
Publisher: N. Peršin]
UDC: 512.552(043.3)
COBISS: 20201992 Link will open in a new window
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Other data

Secondary language: English
Secondary title: Special functional equations on prime rings
Secondary abstract: Special functional equations on prime rings The central object in this thesis are functional equations related to derivations, centralizers and other similary mappings on prime rings. Slovenian mathematicians who first dealt with similar mathers in 80's of the previous century, were J. Vukman, M. Brešar, B. Zalar, B. Hvala and recently also M. Fošner, D. Benkovič, D. Eremita, I. Kosi-Ulbl and A. Fošner. The basic tool has been the theory of functional identities. Let us look into these matters more closely. An additive mapping ▫$D$▫ which maps an arbitrary ring ▫$R$▫ into itself, is called a derivation if ▫$D(xy) = D(x)y + xD(y)$▫ holds for all pairs ▫$x, y$▫ in ▫$R$▫ and is called a Jordan derivation in case ▫$D(x^2) = D(x)x + xD(x)$▫. It is obvious that every derivation is a Jordan derivation. The converse is in general not true. A classical result of Herstein asserts that any Jordan derivation on a prime ring with ▫$char(R)$▫ diferent from ▫$2$▫ is a derivation. In the first part we focus on functional equations connected with derivations. We deal with functional equations ▫$D(x^3) = D(x^2)x + x^2D(x)$▫ and ▫$D(x^3) = D(x)x^2+ xD(x^2)$▫, where ▫$D$▫ is an additive mapping, which maps a ring ▫$R$▫, with suitable characteristic restrictions, into itself. In this case ▫$D$▫ is a derivation. Furthermore, we have found a solution of functional equation ▫$2D(x^{m+n+1})=(m+n+1)(x^mD(x)x^n + x^nD(x)x^m)$▫, where ▫$m$▫ and ▫$n$▫ are some fixed integers and ▫$D$▫ is an additive nonzero mapping, which maps ring ▫$R$▫, with suitable characteristic restrictions, into itself. In this case ▫$D$▫ is a derivation and ▫$R$▫ is commutative ring. Third chapter is about functional equations related to centralizers. An additive mapping ▫$Tv which maps an arbitrary ring ▫$R$▫ into itself, is called a left (right) centralizer in case ▫$T(xy)=T(x)y (T(xy) = xT(y))$▫ holds for all pairs ▫$x, y$▫ in ▫$R$▫. In the first subsection we introduce the solution of the functional equation ▫$2T(x^{m+n+1}) = x^mT(x)x^n + x^nT(x)x^m$▫ on a prime ring with suitable characteristic restrictions, where ▫$m \ge 0$▫ and ▫$n \ge 0$▫ are some fixed integers and ▫$m+n$▫ is not ▫$0$▫. In this case ▫$T$▫ is a two-sided centralizer. An additive mapping ▫$T$▫ which maps an arbitrary ring ▫$R$▫ into itself, is called an ▫$(m,n)$▫-Jordan centralizer in case ▫$(m+n)T(x^2) = mT(x)x+nxT(x)$▫ holds for all ▫$x$▫ in ▫$R$▫, where ▫$m, n$▫ are some fixed integers and ▫$m+n$▫ is not ▫$0$▫. The concept of ▫$(m,n)$▫-Jordan centralizer was introduced by Vukman in 2010. In this article he also proved that any ▫$(m, n)$▫-Jordan centralizer on an arbitrary ring ▫$R$▫, satisfies the relation ▫$2(m+n)2T(xyx) = mnT(x)xy + m(2m + n)T(x)yx - mnT(y)x^2 + 2mnxT(y)x - mnx^2T(y) + n(m + 2n)xyT(x) + mnyxT(x) for all pairs ▫$x, y$▫ in ▫$R$▫. If in this identity we write ▫$y = x$▫, we get another functional equation ▫$2(m+ n)^2T(x^3)=m(2m+ n)T(x)x^2+ 2mnxT(x)x+n(m+ 2n)x^2T(x)$▫, which we treat in the very last part on a prime ring, with suitable charachteristic restrictions, where ▫$m, n$▫ are some fixed integers. We prove that in this case ▫$T$▫ is a two-sided centralizer. We conclude with some open questions on functional equations related to generalized derivations and ▫$(\theta, \phi)$▫-derivations, where ▫$\theta$▫ and ▫$\phi$▫ are automorphisms of ▫$R$▫.
Secondary keywords: functional equations;derivation;centralizer;mapping;prime rings;dissertations;
URN: URN:SI:UM:
Type (COBISS): Doctoral dissertation
Thesis comment: Univ. v Mariboru, Fak. za naravoslovje in matematiko, Oddelek za matematiko in računalništvo
Pages: 89 str.
ID: 8728212