This article continues the study of computable elementary topology started by the author and T. Grubba in 2009 and extends the author's 2010 study of axioms of computable separation. Several computable T3- and Tychonoff separation axioms are introduced and their logical relation is investigated. A number of implications between these axioms are proved and several implications are excluded by counter examples, however, many questions have not yet been answered. Known results on computable metrization of T3-spaces from M. Schr/"oder (1998) and T. Grubba, M. Schr/"oder and the author (2007) are proved under uniform assumptions and with partly simpler proofs, in particular, the theorem that every computably regular computable topological space with non-empty base elements can be embedded into a computable metric space. Most of the computable separation axioms remain true for finite products of spaces.

In the representation approach (TTE) to computable analysis, the representations of an algebraic or topological structure for which the basic predicates and functions become computable are of particular interest. There are, however, many predicates (like equality of real numbers) and functions that areabsolutely non-computable, that is, not computable for any representation. Many of these results can be deduced from a simple lemma. In this article we prove this lemma for multi-representations and apply it to a number of examples. As applications, we show that various predicates and functions on computable measure spaces are absolutely non-computable. Since all the arguments are topological, we prove that the predicates are not relatively open and the functions are not relatively continuous for any multi-representation.

For a partial differential operator $P=\sum _{|\alpha |\leq m}c_{\alpha }D^{\alpha }$ with constant coefficients, a generalized function u is a fundamental solution if $Pu=\delta$, where $\delta$ is the Dirac distribution. In this article, we provide an algorithm which computes a fundamental solution for every such differential operator P on a Turing machine if the input- and output-data are represented canonically.

Although numerous computer programs have been written to compute sets of points which claim to approximate Julia sets, no reliable high precision pictures of non-trivial Julia sets are currently known. Usually, no error estimates are added and even those algorithms which work reliably in theory, become unreliable in practice due to rounding errors and the use of fixed length floating point numbers.In this paper we prove the existence of polynomial time algorithms to approximate the Julia sets of complex functions f(z)=z2+c for |c|

The theory of generalized functions is the foundation of the modern theory of partial differential equations (PDE). As computers are playing an ever-larger role in solving PDEs, it is important to know those operations involving generalized functions in analysis and PDE that can be computed on digital computers. In this article, we introduce natural concepts of computability on test functions and generalized functions, as well as computability on Schwartz test functions and tempered distributions. Type-2 Turing machines are used as the machine model [Weihrauch 2000]. It is shown here that differentiation and integration on distributions are computable operators, and various types of Fourier transforms and convolutions are also computable operators. As an application, it is shown that the solution operator of the distributional inhomogeneous three dimensional wave equation is computable.

We study the computability of the Lebesgue measure of a two-dimensional region that has a polynomial-time computable boundary. It is shown that the two-dimensional measure of the boundary itself completely characterizes the computability of the measure of the interior region. Namely, if a polynomial-time computable, simple, closed curve has measure zero, then its interior region must have a computable measure. Conversely, if such a curve has a positive measure, then the measure of its interior region could be any positive, left r.e. real number.