### Approximate iterative method and the existence of solutions of nonlinear parabolic differential-functional equations

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Let $A=\mathrm{d}/\mathrm{d}\theta $ denote the generator of the rotation group in the space $C\left(\Gamma \right)$, where $\Gamma $ denotes the unit circle. We show that the stochastic Cauchy problem $$\mathrm{d}U\left(t\right)=AU\left(t\right)+f\mathrm{d}{b}_{t},\phantom{\rule{1.0em}{0ex}}U\left(0\right)=0,\phantom{\rule{2.0em}{0ex}}\left(1\right)$$ where $b$ is a standard Brownian motion and $f\in C\left(\Gamma \right)$ is fixed, has a weak solution if and only if the stochastic convolution process $t\mapsto {(f*b)}_{t}$ has a continuous modification, and that in this situation the weak solution has a continuous modification. In combination with a recent result of Brzeźniak, Peszat and Zabczyk it follows that (1) fails to have a weak solution for all...

We consider the second order initial value problem in a Hilbert space, which is a singular perturbation of a first order initial value problem. The difference of the solution and its singular limit is estimated in terms of the small parameter $\epsilon .$ The coefficients are commuting self-adjoint operators and the estimates hold also for the semilinear problem.

We study a linear second order parabolic equation in an open subset of a separable Hilbert space, with the Dirichlet boundary condition. We prove that a probabilistic formula, analogous to one obtained in the finite-dimensional case, gives a solution to this equation. We also give a uniqueness result.

We consider the Fourier first boundary value problem for an infinite system of weakly coupled nonlinear differential-functional equations. To prove the existence and uniqueness of solution, we apply a monotone iterative method using J. Szarski's results on differential-functional inequalities and a comparison theorem for infinite systems.

2000 Mathematics Subject Classification: Primary 46F25, 26A33; Secondary: 46G20In this paper we study the generalized Riemann-Liouville (resp. Caputo) time fractional evolution equation in infinite dimensions. We show that the explicit solution is given as the convolution between the initial condition and a generalized function related to the Mittag-Leffler function. The fundamental solution corresponding to the Riemann-Liouville time fractional evolution equation does not admit a probabilistic...

We consider the initial value problem for an infinite system of differential-functional equations of parabolic type. General operators of parabolic type of second order with variable coefficients are considered and the system is weakly coupled. The solutions are obtained by the monotone iterative method. We prove theorems on weak partial differential-functional inequalities as well the existence and uniqueness theorems in the class of continuous bounded functions and in the class of functions satisfying...

In questo articolo si ottengono stime di Schauder di tipo nuovo per equazioni ellittiche infinito-dimensionali del secondo ordine con coefficienti Hölderiani a valori nello spazio degli operatori Hilbert-Schmidt. In particolare si mostra che la derivata seconda delle soluzioni è Hilbert-Schmidt.