On the complexity of some birational transformations
  Using three different approaches, we analyze the complexity of various birational maps constructed from simple operations (inversions) on square matrices of arbitrary size. The first approach consists in the study of the images of lines, and relies mainly on univariate polynomial algebra, the second approach is a singularity analysis, and the third method is more numerical, using integer arithmetics. Each method has its own domain of application, but they give corroborating results, and lead us to a conjecture on the complexity of a class of maps constructed from matrix inversions. 
Jean Christian Angles D'Auriac (CRTBT), Jean-Marie Maillard (LPTL),   Claude Viallet (LPTHE)