This paper deals with the numerical solution of initial value problems for systems of differential equations with two delay terms. We investigate the stability of adaptations of the θ-methods in the numerical solutio...This paper deals with the numerical solution of initial value problems for systems of differential equations with two delay terms. We investigate the stability of adaptations of the θ-methods in the numerical solution of test equations u'(t) = a 11 u(t) + a12v(t) + b11 u(t - τ1) + b12v(t-τ2,v'(t) = a21 u(t) + a22 v(t) + b21 u(t -τ1,) + b22 v(t -τ2), t>0,with initial conditionsu(t)=u0(t),v(t) =v0(t), t≤0.where aij, bij∈C, τj >0, i,j = 1,2,, and u0(t), v0(t)are continuous and complex valued. Sufficient conditions for the asymptotic stability of test equation are derived. Furthermore, with respect to an appropriate definition of stability for the numerical method, it is proved that the linear θ-method is stable if and only if 1/2≤θ≤1 and the one-leg θ-method is stable if and only if θ= 1.展开更多
A valuable number of works has been published about Hurwitz and Schur polynomials in order to known better their properties. For example it is known that the sets of Hurwitz and Schur polynomials are open and no conve...A valuable number of works has been published about Hurwitz and Schur polynomials in order to known better their properties. For example it is known that the sets of Hurwitz and Schur polynomials are open and no convex sets. Besides, the set of monic Schur polynomials is contractible. Now we study this set using ideas from differential topology, and we prove that the space of Schur complex polynomials with positive leading coefficient, and the space of Hurwitz complex polynomials which leading coefficient having positive real part, have structure of trivial vector bundle, and each space of （Schur complex and real, Hurwitz complex） polynomials has a differential structure diffeomorphic to some known spaces.展开更多
Let l and n be positive integers such that l≥n,and let Gn,l be the Grassmannian which consists of the set of n-dimensionsil subspaces of C^(l),There is a Z-graded algebra isomorphism between the cohomology H*(Gn,l,Z)...Let l and n be positive integers such that l≥n,and let Gn,l be the Grassmannian which consists of the set of n-dimensionsil subspaces of C^(l),There is a Z-graded algebra isomorphism between the cohomology H*(Gn,l,Z)of Gn,l and a natural Z-form B of the Z-graded basic algebra of the type A cyclotomic nilHecke algebraH^(0)l,n=<ψ1,…ψn-1,y1,…,yn>.We show that the isomorphism can be chosen such that the image of each(geometrically defined)Schubert class(a1,...,an)coincides with the basis element bλconstructed by Hu and Liang by purely algebraic method,where 0≤q1≤q2≤…≤an≤l-n with ai∈Z for each i,andλis the l-€-multipartition of n associated to(l+1-(an+n),l+1-(an-1+n-),...,l+1-(a1+1)).A similar correspondence between the Schubert class basis of the cohomology of the Grassmanni-an Gl-n,l and the bλ's basis(λis anl-multipartition of n with each component being either(1)or empty)of the natural Z-form B of the Z-graded basic algebra of H^(0)_(l,n)is also obtained.As an application,we obtain a second version of the Giambelli formula for Schubert classes.展开更多
文摘This paper deals with the numerical solution of initial value problems for systems of differential equations with two delay terms. We investigate the stability of adaptations of the θ-methods in the numerical solution of test equations u'(t) = a 11 u(t) + a12v(t) + b11 u(t - τ1) + b12v(t-τ2,v'(t) = a21 u(t) + a22 v(t) + b21 u(t -τ1,) + b22 v(t -τ2), t>0,with initial conditionsu(t)=u0(t),v(t) =v0(t), t≤0.where aij, bij∈C, τj >0, i,j = 1,2,, and u0(t), v0(t)are continuous and complex valued. Sufficient conditions for the asymptotic stability of test equation are derived. Furthermore, with respect to an appropriate definition of stability for the numerical method, it is proved that the linear θ-method is stable if and only if 1/2≤θ≤1 and the one-leg θ-method is stable if and only if θ= 1.
文摘A valuable number of works has been published about Hurwitz and Schur polynomials in order to known better their properties. For example it is known that the sets of Hurwitz and Schur polynomials are open and no convex sets. Besides, the set of monic Schur polynomials is contractible. Now we study this set using ideas from differential topology, and we prove that the space of Schur complex polynomials with positive leading coefficient, and the space of Hurwitz complex polynomials which leading coefficient having positive real part, have structure of trivial vector bundle, and each space of （Schur complex and real, Hurwitz complex） polynomials has a differential structure diffeomorphic to some known spaces.
基金The research was supported by the National Natural Science Foundation of China(No.11525102).
文摘Let l and n be positive integers such that l≥n,and let Gn,l be the Grassmannian which consists of the set of n-dimensionsil subspaces of C^(l),There is a Z-graded algebra isomorphism between the cohomology H*(Gn,l,Z)of Gn,l and a natural Z-form B of the Z-graded basic algebra of the type A cyclotomic nilHecke algebraH^(0)l,n=<ψ1,…ψn-1,y1,…,yn>.We show that the isomorphism can be chosen such that the image of each(geometrically defined)Schubert class(a1,...,an)coincides with the basis element bλconstructed by Hu and Liang by purely algebraic method,where 0≤q1≤q2≤…≤an≤l-n with ai∈Z for each i,andλis the l-€-multipartition of n associated to(l+1-(an+n),l+1-(an-1+n-),...,l+1-(a1+1)).A similar correspondence between the Schubert class basis of the cohomology of the Grassmanni-an Gl-n,l and the bλ's basis(λis anl-multipartition of n with each component being either(1)or empty)of the natural Z-form B of the Z-graded basic algebra of H^(0)_(l,n)is also obtained.As an application,we obtain a second version of the Giambelli formula for Schubert classes.
