In the paper, we consider the problem of computing visibility information on digital terrain models. Visibility problems on polyhedral terrains are classi ed according to the kind of visibility information computed into point visibility, line visibility and region visibility. A survey of the state-of-the-art of the algorithms for computing visibility is presented, according to the classi cation...

We regret to record the death of Dr. P. P. Johnson, of Yatton, .after a long and painful illness, borne with much fortitude. Dr. Johnson was 57 years of age, and was educated at Sedbergh, afterwards proceeding to Edinburgh University, where he took his degree in 1877. He practised for over nine years at Littleborough, in Lancashire, and for a short time in Starbotton, Yorkshire, and came to Yat...

Aslam presents an algorithm he claims will count the number of perfect matchings in any incomplete bipartite graph with an algorithm in the function-computing version of NC, which is itself a subset of FP. Counting perfect matchings is known to be #P-complete; therefore if Aslam's algorithm is correct, then NP=P. However, we show that Aslam's algorithm does not correctly count the number of per...

This report studies problems coming from three di erent domains of theoretical computer science: Clique versus Independent set in communication complexity, the Alon-SaksSeymour conjecture in graph coloring and the stubborn problem in constraint satisfaction problem. Each problem admits a quasi-polynomial size solution, meaning of size n where n is the parameter, and the problem is to nd a polyn...