From: Vasilis Vavourakis <vasvav@gm...>  20090319 16:39:54

John you are right, the matrix is not DENSE, it's banded ;) i just typed the class of matrix i declared in my assembly function! 2009/3/19 Roy Stogner <roystgnr@...>: > > On Thu, 19 Mar 2009, Vasilis Vavourakis wrote: > >> i don't know if this might sound a silly question BUT i want to >> perform the inversion of a "DenseMatrix" of a system... > > There's a reason why the Matlab "inv" help page begins: "In practice, > it is seldom necessary to form the explicit inverse of a matrix"  and > that's talking with dense matrices in mind! For large sparse matrices > inversion is usually much, much less efficient than iterative solves. > >> to be more specific, i want to implement the "arclength" procedure >> for nonlinear structural problems. > > Check out John Peterson's dissertation. He did arclength > continuation for some nonlinear fluid mechanics problems, and he > contributed the physicsindpendent components of his code back to > libMesh. You basically augment the nonlinear system with a single > scalar arclength variable and solve an expanded problem with a weird > (but still sparse!) operator structure. Roy, you are right too, the simplest way to implement the arclength procedure is to augment the system with one "constraint" equation... the problem is that it's not that clear to me (i'm not that a libmesh expert) to add another "one" degreeoffreedom in the system! however i'll try to have a look at John dissertation :) although Crisfield's book seems to be very clarifying to that issue. many thanks again for the prompt replies >  > Roy > 