An educational computational application for analyzing plane stress problems oriented to engineering students called EsfPlano2D is presented motivate study the subject and strengthen didactic strategies in classroom. The assists step-by-step calculation of problems, which a fundamental topic teaching Mechanics Materials careers. computer program developed Fortran, linked free Computer Algebra S...

1 Let there be given n points in the plane. Denote by t i the number of lines which contain exactly i of the points (2 < i < n). The properties of the set {ti } have been studied a great deal. For example, there is the classical result of Gallai and Sylvester : Assume to = 0 (i .e ., the points are not all on one line) ; then t2 > 0. For the history of this problem see, e.g ., Motzkin [6] and E...

Consider a 0/1 integer program min{c T x : Ax ≥ b, x ∈ {0, 1} n } where A is nonnegative. We show that if the number of minimal covers of Ax ≥ b is polynomially bounded, then there is a polynomially large relaxation whose value is arbitrarily close to being at least as good as that given by the rank-r closure, for any fixed r. A special case of this result is that given by set-covering problems...