hi Matt, I used to discuss with somebody about SNES for nonlinear equation. One can use -snes_mf_operator for matrix free calculation. As far as I know, SNES uses a Newton-Kryplov Method. In each Newton, one has to solve a linear equation, which is : residual = Jacobian * delt_u If I can solve the linear equation in a iterative way in Kryplov space, then I only need to optimise Jacobian*delt_u - residual The matrix vector multiplication can be expressed through the gradient calculation for residual. That's why we can forget the Jacobian matrix. The method is generally called Jacobian free Newton Kryplov mehtod (JFNK). You must know it. Actually, that's the way snes works with -snes_mf. Here, we define the function SNESSetFunction(). And as argument, we give the calculation of residual. I wrote so much only because of the continuity of the context. Now my question is, if the SNES method includes a JFNK method to solve the linear equation, why can't I use it for my linear equation directly? And how?
thanx pan --- Matthew Knepley <knepley at gmail.com> wrote: > On Mon, Mar 3, 2008 at 11:05 AM, li pan > <li76pan at yahoo.com> wrote: > > Dear all, > > If I want to solve a linear equation in matrix > free > > scheme, how is the command line argument? I only > know > > for nonlinear solver it is _snes_mf > > What do you mean here? How do you have linear > equations without > a matrix? If you mean that you would only like to > specify the action > of the operator, you should use MATSHELL. > > Matt > > > thanx > > > > pan > > > > > > > > > ____________________________________________________________________________________ > > Looking for last minute shopping deals? > > Find them fast with Yahoo! Search. > http://tools.search.yahoo.com/newsearch/category.php?category=shopping > > > > > > > > -- > What most experimenters take for granted before they > begin their > experiments is infinitely more interesting than any > results to which > their experiments lead. > -- Norbert Wiener > > ____________________________________________________________________________________ Never miss a thing. Make Yahoo your home page. http://www.yahoo.com/r/hs
