Decoupled formulation of constraints on adaptive hanging nodes in EUROPLEXUS

The present report introduces the possibility of formulating the constraints on so-called "hanging" nodes which arise in adaptivity in a decoupled manner, rather than by using the standard, fully coupled treatment. The scope is to try reduce the CPU time required in some complex 3D applications, including those using adaptivity in shell elements. In these applications, when the number of hanging constraints may become huge and the (implicit) solution of the fully coupled problem may either require a large CPU time, if using the standard solver (Cholesky method), or may occasionally fail when using special solvers which are in principle more efficient