Anahí Gajardo

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The virtual ant introduced by C. Langton has an interesting behavior, which has been studied in several contexts. Here we give a construction to calculate any boolean circuit with the trajectory of a single ant. This proves the P-hardness of the system and implies, through the simulation of one dimensional cellular automata and Turing machines, the(More)
Abstract. We introduce a concept of similarity between vertices of directed graphs. Let GA and GB be two directed graphs with respectively nA and nB vertices. We define a nB × nA similarity matrix S whose real entry sij expresses how similar vertex j (in GA) is to vertex i (in GB) : we say that sij is their similarity score. The similarity matrix can be(More)
We have performed a prospective, randomized, double-blind clinical study to assess the efficacy of ondansetron, droperidol, or both, in preventing postoperative emesis. We studied 242 patients undergoing biliary or gynaecological surgery under general anaesthesia. Shortly before induction of anaesthesia, patients received: saline i.v. (group I, n = 62);(More)
Langton’s ant is a simple discrete dynamical system, with a surprisingly complex behavior. We study its extension to general planar graphs. First we give some relations between characteristics of finite graphs and the dynamics of the ant on them. Then we consider the infinite bi-regular graphs of degrees 3 and 4, where we prove the universality of the(More)
We introduce a concept of similarity between vertices of directed graphs. Let GA and GB be two directed graphs with, respectively, nA and nB vertices. We define an nB ×nA similarity matrix S whose real entry sij expresses how similar vertex j (in GA) is to vertex i (in GB): we say that sij is their similarity score. The similarity matrix can be obtained as(More)
O ne of the first models of artificial life, proposed back in the 1980s by Christopher Langton, founder of the field, was the virtual ant [1,2]. This simple cellular automaton is defined on the square grid in the following way: each square (“cell”) of the grid can be in one of two states, white or black, and the ant is represented by a short arrow that(More)
Together with the concept of reversibility, another relevant physical notion is time-symmetry, which expresses that there is no way of distinguishing between backward and forward time directions. This notion, found in physical theories, has been neglected in the area of discrete dynamical systems. Here we formalize it in the context of cellular automata and(More)