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From: John Peterson <peterson@cf...>  20060323 17:19:44

Shengli Xu writes: > On 3/23/06, Shengli Xu <shengli.xu.xu@...> wrote: > > > > Dear Developers and Users, > > I want to get the node's coordinate from the node vector. > > // define node vector > > typedef std::vector<Node*> evec; > > evec Nevec; > > { > > // add some node to Nevec through Nevec.push_back() > > } > > for(evec::iterator it = Nevec.begin(); it !=Nevec.end(); ++it){ > > > > // Is this right to get the node coordinate? Compile shows that is > error. > > > const Real nx = (*it)(0); > > const Real ny = (*it)(1); Dereferencing the iterator with *it returns a Node*. Thus you can do (*it)>operator()(0); // awkward! Or (*(*it))(0) // holy parentheses batman! Or Node *node = *it; (*node)(0); John 
From: John Peterson <peterson@cf...>  20060323 17:07:18

David Xu writes: > Hi, > > How can I perform Matrixvector multiplication for SparseMatrix? The > SparseMatrix class doesn't seem to have such capability. Hi, What you need is the add_vector(x,A) routine in numeric_vector.h J 
From: Benjamin S. Kirk <benjamin.kirk@na...>  20060323 15:01:27

On Thu, 20060323 at 08:27 0600, Roy Stogner wrote: > On Thu, 23 Mar 2006, li pan wrote: > > > The penalty method was used to set boundary condition > > in ex13. Can I use DenseMatrix::condense() in stead of > > penalty method? > > In general, not easily. Even if you know the nodal values implied by > your boundary conditions (which may not be easy for nonLagrange > elements), what happens when you have boundary nodes that are on > nonboundary elements? (picture a triangulated domain, for example, > or an interior corner on a mesh of quads). You'd need to use > condense() on every element matrix that included your boundary node, > which means you'd have to store a pernode "I'm on the boundary" flag > somewhere; libMesh only keeps track of boundary element sides. > Agreed. You can use the condense method, but you have to avoid the pitfall Roy describes. However, the BoundaryInfo class does keep track of boundary nodes for the boundary sides it tracks. The only possible problem is when you have, for example, a corner node which lives on two sides with two separate BC ids. This does give you the option of using the condense method for Lagrange elements, but as Roy points out you can no longer restrict your boundary condition applications to elements with a side on the boundary. See http://libmesh.sourceforge.net/doxygen/classBoundaryInfo.html#a6 Now, since only level0 elements have their side BCs stored then only their nodes will get added in this automatic way. But, as a preprocessing step, you could loop through all active elements on the boundary and add their nodes to the BoundaryInfo class. > > Another simple question, how to calculate invert matrix in libmesh? > > There is no inverse, I'm afraid; nobody has needed anything more than > linear system solves with DenseMatrix. It's rare that you really need > a matrix inverse, but if you do you can call lu_solve() or > cholesky_solve() with each of N unit vectors to build one. Roy's right here too ;) To quote one of my professors, "we only invert matrices under the penalty of death." Also, multiple subsequent lu_solve()'s will only perform the O(n^3) factorization once and then just do a series of O(n^2) back substitutions. See http://libmesh.sourceforge.net/doxygen/classDenseMatrix.html#a19 Ben 
From: Roy Stogner <roystgnr@ic...>  20060323 14:29:53

On Thu, 23 Mar 2006, Shengli Xu wrote: > On 3/23/06, Shengli Xu <shengli.xu.xu@...> wrote: >> >> Dear Developers and Users, >> I want to get the node's coordinate from the node vector. >> // define node vector >> typedef std::vector<Node*> evec; >> evec Nevec; >> { >> // add some node to Nevec through Nevec.push_back() >> } >> for(evec::iterator it = Nevec.begin(); it !=Nevec.end(); ++it){ >> > > // Is this right to get the node coordinate? Compile shows that is > error. > >> const Real nx = (*it)(0); >> const Real ny = (*it)(1); > No; (it) is an iterator to pointers to Nodes; (*it) is a pointer to Node; you want (**it)(0) and (**it)(1) to operate on the Nodes themselves.  Roy Stogner 
From: Roy Stogner <roystgnr@ic...>  20060323 14:28:06

On Thu, 23 Mar 2006, li pan wrote: > The penalty method was used to set boundary condition > in ex13. Can I use DenseMatrix::condense() in stead of > penalty method? In general, not easily. Even if you know the nodal values implied by your boundary conditions (which may not be easy for nonLagrange elements), what happens when you have boundary nodes that are on nonboundary elements? (picture a triangulated domain, for example, or an interior corner on a mesh of quads). You'd need to use condense() on every element matrix that included your boundary node, which means you'd have to store a pernode "I'm on the boundary" flag somewhere; libMesh only keeps track of boundary element sides. > Another simple question, how to calculate invert matrix in libmesh? There is no inverse, I'm afraid; nobody has needed anything more than linear system solves with DenseMatrix. It's rare that you really need a matrix inverse, but if you do you can call lu_solve() or cholesky_solve() with each of N unit vectors to build one.  Roy 
From: Roy Stogner <roystgnr@ic...>  20060323 14:18:47

On Thu, 23 Mar 2006, li pan wrote: > I need a tensor of order 4. Is this defined in > libmesh? No; after implementing 2nd order tensors I realized that even those were hard to generalize efficiently due to possible symmetry. Even if you've got a 4th order tensor conceptually, it's very unlikely that you've got the 81 independent coefficients that such a tensor would require in a general implementation.  Roy Stogner 
From: David Xu <dxu@my...>  20060323 13:54:15

Hi, How can I perform Matrixvector multiplication for SparseMatrix? The SparseMatrix class doesn't seem to have such capability. Thanks, David 
From: Shengli Xu <shengli.xu@gm...>  20060323 12:19:15

On 3/23/06, Shengli Xu <shengli.xu.xu@...> wrote: > > Dear Developers and Users, > I want to get the node's coordinate from the node vector. > // define node vector > typedef std::vector<Node*> evec; > evec Nevec; > { > // add some node to Nevec through Nevec.push_back() > } > for(evec::iterator it =3D Nevec.begin(); it !=3DNevec.end(); ++it){ > // Is this right to get the node coordinate? Compile shows that is error. > const Real nx =3D (*it)(0); > const Real ny =3D (*it)(1); > Cheers, ShengliXu 
From: Shengli Xu <shengli.xu@gm...>  20060323 12:15:34

Dear Developers and Users, I want to get the node's coordinate from the node vector. // define node vector typedef std::vector<Node*> evec; evec Nevec; { // add some node to Nevec through Nevec.push_back() } for(evec::iterator it =3D Nevec.begin(); it !=3DNevec.end(); ++it){ const Real nx =3D (*it)(0); const Real ny =3D (*it)(1); 
From: li pan <li76pan@ya...>  20060323 11:37:53

Dear all, The penalty method was used to set boundary condition in ex13. Can I use DenseMatrix::condense() in stead of penalty method? Another simple question, how to calculate invert matrix in libmesh? best pan __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com 
From: li pan <li76pan@ya...>  20060323 10:34:45

Dear everyone, I need a tensor of order 4. Is this defined in libmesh? best pan __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com 