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From: Roy Stogner <roystgnr@ic...>  20060223 21:39:09

On Thu, 23 Feb 2006, John Peterson wrote: > According to the source code, it's something like this: > > order p = # of points 2p1 > ===== =============== ==== > CONSTANT,FIRST 1 1 > SECOND 3 5 > THIRD 4 7 No, no, you're looking at triangle quadratures  the "2p1" rule only applies on line segments. Even in the code for triangles, it looks to me like the rules labeled "exact for quadratics", "exact for cubics", etc. should be exact when integrating quadratics, cubics, etc. not products of them. I'm committing a CVS change to the quadrature_gauss.h comments to say so.  Roy 
From: John Peterson <peterson@cf...>  20060223 21:24:51

Roy Stogner writes: > On Thu, 23 Feb 2006, li pan wrote: > > Ben, John, is our QGauss documentation wrong? It says, "Gauss > quadrature rules of order p have the property of integrating > polynomials of degree 2p1 exactly.", but that's not true. That > sounds like the theorem for a 1D Gauss rule with p points, but looking > in the code, we aren't using the Order argument to choose a number of > points, we're using it to choose what degree of polynomial to exactly > integrate. The documentation is wrong. According to the source code, it's something like this: order p = # of points 2p1 ===== =============== ==== CONSTANT,FIRST 1 1 SECOND 3 5 THIRD 4 7 I think it's based on computing entries in the "mass matrix" M_ij = \int (phi_i * phi_j) dx. So, I think a "SECOND" order rule will compute M_ij exactly if both phi_i and phi_j are quadratic polynomials. A "THIRD" order rule will compute M_ij exactly if both phi_i and phi_j are cubic polys. etc. J 
From: Roy Stogner <roystgnr@ic...>  20060223 20:22:04

On Thu, 23 Feb 2006, li pan wrote: > thanks for your suggestion. I think I can try to do > the integration like with hex mesh. Another simple > question. If I'm using Tet4, and considering u v w > components (variables), and all the components have > order one, can I use QGauss(SECOND)? If you're integrating products of two linear functions, then any rule that exactly integrates quadratics will work for you  QGauss(SECOND) is the cheapest such rule. Of course, I don't know exactly what you're integrating  if you're just solving a Laplacian problem and only need to integrate products of gradients, then all your integrals except the boundary integrals are elementwise constant, and QGauss(CONSTANT) will give you the same results with one quadrature point instead of four. If you're solving a nonlinear problem or a problem with variable coefficients, then getting exact integrals from a quadrature rule may be impossible, and even if QGauss(SECOND) doesn't ruin your O(h^2) accuracy you may want to experiment with higher rules to get a better constant in front of that h^2. Ben, John, is our QGauss documentation wrong? It says, "Gauss quadrature rules of order p have the property of integrating polynomials of degree 2p1 exactly.", but that's not true. That sounds like the theorem for a 1D Gauss rule with p points, but looking in the code, we aren't using the Order argument to choose a number of points, we're using it to choose what degree of polynomial to exactly integrate.  Roy 
From: Kirk, Benjamin \(JSCEG\) <benjamin.kirk1@na...>  20060223 15:23:36

I'd be happy to help here too, but there is another option you could consider. PETSc says they can interface directly with UMFPACK. In that case, you simply need to build PETSc such that it uses UMFPACK internally and then you should have access to (at leas a subset of) the UMFPACK sparse directly. The standard PETSc allows for "pc_type direct" which does a dense direct LU factorization and then uses it as the "preconditioner" in an iterative method (which will then converge in 1 iteration). This only works on serial problems, mind you, but it looks like UMFPACK is serial as well. If you install PETSc with UMFPACK support I would guess you'd get something like "pc_type umfpack" which would then build the "preconditioner" using UMFPACK's Unsymmetric sparse multifrontal method. The only reason I mention it is because it may be the path of least resistance, especially if UMFPACK is relegated to serial problems only. Adding a new solver interface is fairly straightforward but time consuming, and it is a lot of work to go through for a solver which will only work on serial problems. Ben Original Message From: libmeshusersadmin@... [mailto:libmeshusersadmin@...] On Behalf Of John Peterson Sent: Thursday, February 23, 2006 8:47 AM To: Blome Mark Cc: Libmeshusers@... Subject: [Libmeshusers] direct solver Blome Mark writes: > > I would like to use a direct sparse matrix solver package within > libmesh (for example umfpack, pardiso or thelike). > Am I right that I have to implement an interface for the solver > package by deriving from the class LinearSolver (linear_solver.h)? > Are there any pitfalls I should be aware of ? How do I include the > solver package into the libmesh Makefile so it will get linked > correctly? Did anybody alreay implement a direct solver interface ? You might get some hints from the Petsc and Laspack implementations of the LinearSolver interface. Some things you will probably need are: 1.) UMF_Matrix derived from SparseMatrix 2.) UMF_Vector derived from NumericVector 3.) UMF_Interface as you mentioned This sounds like an interesting project. If UMF is open source, and small enough, we can distribute it directly in libmesh's contrib directory. Otherwise, you will need 4.) configure tests, etc. I think we can help with 1.)  4.) if you do end up trying to do this. J  This SF.Net email is sponsored by xPML, a groundbreaking scripting language that extends applications into web and mobile media. Attend the live webcast and join the prime developer group breaking into this new coding territory! http://sel.asus.falkag.net/sel?cmd=3Dlnk&kid=3D110944&bid=3D241720&dat=3D= 121642 _______________________________________________ Libmeshusers mailing list Libmeshusers@... https://lists.sourceforge.net/lists/listinfo/libmeshusers 
From: John Peterson <peterson@cf...>  20060223 14:47:22

Blome Mark writes: > > I would like to use a direct sparse matrix solver package within > libmesh (for example umfpack, pardiso or thelike). > Am I right that I have to implement an interface for the solver > package by deriving from the class LinearSolver (linear_solver.h)? > Are there any pitfalls I should be aware of ? How do I include the > solver package into the libmesh Makefile so it will get linked > correctly? Did anybody alreay implement a direct solver interface ? You might get some hints from the Petsc and Laspack implementations of the LinearSolver interface. Some things you will probably need are: 1.) UMF_Matrix derived from SparseMatrix 2.) UMF_Vector derived from NumericVector 3.) UMF_Interface as you mentioned This sounds like an interesting project. If UMF is open source, and small enough, we can distribute it directly in libmesh's contrib directory. Otherwise, you will need 4.) configure tests, etc. I think we can help with 1.)  4.) if you do end up trying to do this. J 
From: li pan <li76pan@ya...>  20060223 13:27:55

Hi Roy and John, thanks for your suggestion. I think I can try to do the integration like with hex mesh. Another simple question. If I'm using Tet4, and considering u v w components (variables), and all the components have order one, can I use QGauss(SECOND)? best regards pan On Wed, 22 Feb 2006, li pan wrote: > I realized all the example which include an assemble() > function are written for square or hex. Has anyone got > a example for tetrahedron? It's not clear for me how > to do volume integration and surface integration in > the case of tetrahedron. It's exactly the same as area integration and edge integration for the 2D cases. I've got an altered 2D+3D example 15 that I could send you if you want (or I could finally get around to cleaning it up and committing it to CVS...), but it's not going to tell you much  the assemble function is exactly the same no matter whether the mesh is CloughTocher triangles, Hermite rectangles, or Hermite cubes.  Roy __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com 
From: Blome Mark <blome@au...>  20060223 12:49:30

Hi everybody, I would like to use a direct sparse matrix solver package within libmesh = (for example umfpack, pardiso or thelike).=20 Am I right that I have to implement an interface for the solver package = by deriving from the class LinearSolver (linear_solver.h)? Are there any = pitfalls I should be aware of ? How do I include the solver package into = the libmesh Makefile so it will get linked correctly? Did anybody alreay = implement a direct solver interface ?=20 Thanks for any help on this, Mark=20 
From: Shengli Xu <shengli.xu.xu@gm...>  20060223 10:09:43

Dear all, I need to consider the pressure load. But I don't know how to form the inpu= t file such as .unv or .xda considering the pressure. The example laplace.tar.bz2 supported by Ondrej Certik on the libmesh wiki. But there i= s an error when run ./mesh. the error is :  ... Info : Writing mesh file 't1.msh' Info : Mesh 2D complete (0.028995 s) Info : Writing mesh file 't1.msh' Info : 411 nodes Info : 1537 elements Info : Wrote mesh file 't1.msh' reading... Traceback ( most recent call last): File "./msh2libmesh", line 28, in ? m.readmsh("t1.msh",b, False,False) TypeError: readmsh() takes at most 4 arguments (5 given) I doubt that "m.readmsh("t1.msh",b,False,False)" just has 4 argumets. why i= t display "5 given"? best ShengliXu 