2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/161933Numerically exact investigations of interacting spin systems provide a major tool for an understanding of their magnetic properties. For medium size systems the approximate Lanczos diagonalization is the most common method. In this article we suggest two improvements: efficient basis coding in subspaces and simple restructuring for openMP parallelization.9 pages, 2 figues, submitted to Journal of Computational PhysicsStrongly Correlated ElectronsStatistical Mechanicstext