This special issue of Concurrency and Computation: Practice and Experience contains revised and extended versions of selected papers presented at the 11th International Conference on Parallel Processing and Applied Mathematics, PPAM 2015, which was held on September 6 to 9, 2015, in Krakow, Poland.PPAM is a biennial series of international conferences dedicated to exchanging ideas between researchers involved in parallel and distributed computing, including theory and applications, as well as applied and computational mathematics. The focus of PPAM 2015 was on models, algorithms, and software tools that facilitate efficient and convenient use of modern parallel and distributed computing systems, as well as on large-scale applications, including data-intensive problems. This meeting gathered more than 190 participants from 33 countries. A strict reviewing process, with each submission reviewed at least three times, resulted in acceptance of 111 contributed papers with the acceptance rate of 57%. The accepted papers were presented at the regular tracks of the PPAM 2015 conference, as well as during the workshops that were important and integral parts of the PPAM 2015 meeting.Based on the results of the reviews, selected papers were recommended for a special journal issue. Besides quality, another important goal that influenced the paper selection was a maximum possible thematic consistency of the issue. The focus of this special issue is on algorithmic advances to better match the software properties to the targeted parallel architecture. These advances vary from general, like increasing potential reuse of a part of computation, to specific for a particular architecture, eg, using GPUs or with multi-core and many-core processors, or specific applications, such as spherical Delaunay triangulations, or visualization of complex networks. The authors were contacted after the conference and invited to submit revised and extended versions of their papers. These new versions were reviewed independently by three reviewers. Finally, nine contributions were accepted for publication. They are summarized below.Paper [1] focuses on LU factorization, which is a recurrent operation in scientific and engineering applications used to solve linear systems. In particular, the authors adapt the Gauss-Huard algorithm that has been introduced as an efficient solution for modern platforms equipped with accelerators to improve reusing of computations in this algorithm. This approach was evaluated on the solution of Lyapunov matrix equations via the LRCF-ADI method and validated on three benchmarks. In future work, the authors plan to design a heuristic for choosing the optimal block size and to integrate their solution with the mixed precision techniques to further accelerate the Lyapunov solver.An efficient algorithm for solving dense symmetric indefinite systems on GPUs is presented in the work of Baboulin et al. [2]. The critical challenge on these types of computations on hybrid CPU/GPU is to keep to minimum the expensive data transf...