Transitive Closure of Infinite Graphs and its Applications

dc.contributor.authorKelly, Wayneen_US
dc.contributor.authorPugh, Williamen_US
dc.contributor.authorRosser, Evanen_US
dc.contributor.authorShpeisman, Tatianaen_US
dc.description.abstractInteger tuple relations can concisely summarize many types of information gathered from analysis of scientific codes. For example they can be used to precisely describe which iterations of a statement are data dependent of which other iterations. It is generally not possible to represent these tuple relations by enumerating the related pairs of tuples. For example, it is impossible to enumerate the related pairs of tuples in the relation {[i] -> [i+2] | 1 <= i <= n-2}. Even when it is possible to enumerate the related pairs of tuples, such as for the relation {[i,j] -> [i',j'] | 1 <= i,j,i',j' <= 100}, it is often not practical to do so. We instead use a closed form description by specifying a predicate consisting of affine constraints on the related pairs of tuples. As we just saw, these affine constraints can be parameterized, so what we are really describing are infinite families of relations (or graphs). Many of our applications of tuple relations rely heavily on an operation called transitive closure. Computing the transitive closure of these "infinite graphs" is very different from the traditional problem of computing the transitive closure of a graph whose edges can be enumerated. For example, the transitive closure of the first relation above is the relation {[i] -> [i'] | exists beta s.t. i'-i = 2beta and 1 <= i <= i' <= n}. As we will prove, this computation is not computable in the general case. We have developed algorithms that produce exact results in most commonly occurring cases and produce upper or lower bounds (as necessary) in the other cases. This paper will describe our algorithms for computing transitive closure and some of its applications such as determining which inter-processor synchronizations are redundant. (Also cross-referenced as UMIACS-TR-95-48)en_US
dc.format.extent234749 bytes
dc.relation.isAvailableAtDigital Repository at the University of Marylanden_US
dc.relation.isAvailableAtUniversity of Maryland (College Park, Md.)en_US
dc.relation.isAvailableAtTech Reports in Computer Science and Engineeringen_US
dc.relation.isAvailableAtUMIACS Technical Reportsen_US
dc.relation.ispartofseriesUM Computer Science Department; CS-TR-3457en_US
dc.relation.ispartofseriesUMIACS; UMIACS-TR-95-48en_US
dc.titleTransitive Closure of Infinite Graphs and its Applicationsen_US
dc.typeTechnical Reporten_US


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