You can subscribe to this list here.
2003 
_{Jan}

_{Feb}

_{Mar}

_{Apr}

_{May}

_{Jun}

_{Jul}

_{Aug}

_{Sep}
(2) 
_{Oct}
(2) 
_{Nov}
(27) 
_{Dec}
(31) 

2004 
_{Jan}
(6) 
_{Feb}
(15) 
_{Mar}
(33) 
_{Apr}
(10) 
_{May}
(46) 
_{Jun}
(11) 
_{Jul}
(21) 
_{Aug}
(15) 
_{Sep}
(13) 
_{Oct}
(23) 
_{Nov}
(1) 
_{Dec}
(8) 
2005 
_{Jan}
(27) 
_{Feb}
(57) 
_{Mar}
(86) 
_{Apr}
(23) 
_{May}
(37) 
_{Jun}
(34) 
_{Jul}
(24) 
_{Aug}
(17) 
_{Sep}
(50) 
_{Oct}
(24) 
_{Nov}
(10) 
_{Dec}
(60) 
2006 
_{Jan}
(47) 
_{Feb}
(46) 
_{Mar}
(127) 
_{Apr}
(19) 
_{May}
(26) 
_{Jun}
(62) 
_{Jul}
(47) 
_{Aug}
(51) 
_{Sep}
(61) 
_{Oct}
(42) 
_{Nov}
(50) 
_{Dec}
(33) 
2007 
_{Jan}
(60) 
_{Feb}
(55) 
_{Mar}
(77) 
_{Apr}
(102) 
_{May}
(82) 
_{Jun}
(102) 
_{Jul}
(169) 
_{Aug}
(117) 
_{Sep}
(80) 
_{Oct}
(37) 
_{Nov}
(51) 
_{Dec}
(43) 
2008 
_{Jan}
(71) 
_{Feb}
(94) 
_{Mar}
(98) 
_{Apr}
(125) 
_{May}
(54) 
_{Jun}
(119) 
_{Jul}
(60) 
_{Aug}
(111) 
_{Sep}
(118) 
_{Oct}
(125) 
_{Nov}
(119) 
_{Dec}
(94) 
2009 
_{Jan}
(109) 
_{Feb}
(38) 
_{Mar}
(93) 
_{Apr}
(88) 
_{May}
(29) 
_{Jun}
(57) 
_{Jul}
(53) 
_{Aug}
(48) 
_{Sep}
(68) 
_{Oct}
(151) 
_{Nov}
(23) 
_{Dec}
(35) 
2010 
_{Jan}
(84) 
_{Feb}
(60) 
_{Mar}
(184) 
_{Apr}
(112) 
_{May}
(60) 
_{Jun}
(90) 
_{Jul}
(23) 
_{Aug}
(70) 
_{Sep}
(119) 
_{Oct}
(27) 
_{Nov}
(47) 
_{Dec}
(54) 
2011 
_{Jan}
(22) 
_{Feb}
(19) 
_{Mar}
(92) 
_{Apr}
(93) 
_{May}
(35) 
_{Jun}
(91) 
_{Jul}
(32) 
_{Aug}
(61) 
_{Sep}
(7) 
_{Oct}
(69) 
_{Nov}
(81) 
_{Dec}
(23) 
2012 
_{Jan}
(64) 
_{Feb}
(95) 
_{Mar}
(35) 
_{Apr}
(36) 
_{May}
(63) 
_{Jun}
(98) 
_{Jul}
(70) 
_{Aug}
(171) 
_{Sep}
(149) 
_{Oct}
(64) 
_{Nov}
(67) 
_{Dec}
(126) 
2013 
_{Jan}
(108) 
_{Feb}
(104) 
_{Mar}
(171) 
_{Apr}
(133) 
_{May}
(108) 
_{Jun}
(100) 
_{Jul}
(93) 
_{Aug}
(126) 
_{Sep}
(74) 
_{Oct}
(59) 
_{Nov}
(145) 
_{Dec}
(93) 
2014 
_{Jan}
(38) 
_{Feb}
(45) 
_{Mar}
(26) 
_{Apr}
(41) 
_{May}
(125) 
_{Jun}
(70) 
_{Jul}
(61) 
_{Aug}
(66) 
_{Sep}
(60) 
_{Oct}
(110) 
_{Nov}
(27) 
_{Dec}
(30) 
2015 
_{Jan}
(43) 
_{Feb}
(67) 
_{Mar}
(71) 
_{Apr}
(92) 
_{May}
(39) 
_{Jun}
(15) 
_{Jul}
(46) 
_{Aug}
(63) 
_{Sep}
(84) 
_{Oct}
(82) 
_{Nov}
(69) 
_{Dec}
(45) 
2016 
_{Jan}
(92) 
_{Feb}
(91) 
_{Mar}
(148) 
_{Apr}
(43) 
_{May}
(58) 
_{Jun}
(117) 
_{Jul}
(92) 
_{Aug}
(140) 
_{Sep}
(49) 
_{Oct}
(33) 
_{Nov}
(85) 
_{Dec}
(40) 
2017 
_{Jan}
(33) 
_{Feb}

_{Mar}

_{Apr}

_{May}

_{Jun}

_{Jul}

_{Aug}

_{Sep}

_{Oct}

_{Nov}

_{Dec}

S  M  T  W  T  F  S 







1

2

3

4
(1) 
5
(1) 
6

7
(8) 
8

9

10
(5) 
11
(6) 
12
(2) 
13
(1) 
14
(1) 
15
(1) 
16

17

18

19

20

21

22

23

24

25
(1) 
26

27

28

29

30

31






From: Steffen Petersen <steffen.petersen@tu...>  20050107 22:21:29

Ups, I just saw that a different connectivity is used for gmv output. Hence, element one, three, five, and six are likely to cause a negative Jacobian. Steffen Pollini Andrea wrote: > On Friday 07 January 2005 15:27, KIRK, BENJAMIN (JSCEG) (NASA) wrote: > >>A negative Jacobian occurs when you have an overlydistorted or inverted >>element. It can also be caused by having elements numbered in a >>nonconsistent manner, e.g. clockwise instead of counterclockwise. >> >>Where did your mesh come from? If it is small, perhaps you can post it and >>I can take a look? >> >> > > > Hi Ben, > the mesh is a cube divided into 6 tetrahedra, and I have build it by > hand... after I uniformly refine it. > > the mesh is below... > > > > gmvinput ascii > > nodes 8 > 0 0 1 1 0 0 1 1 > 0 1 0 1 0 1 0 1 > 0 0 0 0 1 1 1 1 > > cells 6 > tet 4 > 1 4 8 3 > tet 4 > 1 7 8 3 > tet 4 > 1 7 8 5 > tet 4 > 1 4 8 2 > tet 4 > 1 6 8 2 > tet 4 > 1 6 8 5 > > material 1 0 > proc_0 > 1 > 1 > 1 > 1 > 1 > 1 > > > endgmv > > 
From: Steffen Petersen <steffen.petersen@tu...>  20050107 21:03:41

You can check your element definitions with the documentation of class Tet4. All tetrahedral elements have to be defined in this way: TET4: 3 o /\ /  \ /  \ 0 o......o 2 \  / \  / \/ o 1 In the example mesh you sent below it looks as if e.g. the second element will lead to a negative Jacobian. Steffen Pollini Andrea wrote: > On Friday 07 January 2005 15:27, KIRK, BENJAMIN (JSCEG) (NASA) wrote: > >>A negative Jacobian occurs when you have an overlydistorted or inverted >>element. It can also be caused by having elements numbered in a >>nonconsistent manner, e.g. clockwise instead of counterclockwise. >> >>Where did your mesh come from? If it is small, perhaps you can post it and >>I can take a look? >> >> > > > Hi Ben, > the mesh is a cube divided into 6 tetrahedra, and I have build it by > hand... after I uniformly refine it. > > the mesh is below... > > > > gmvinput ascii > > nodes 8 > 0 0 1 1 0 0 1 1 > 0 1 0 1 0 1 0 1 > 0 0 0 0 1 1 1 1 > > cells 6 > tet 4 > 1 4 8 3 > tet 4 > 1 7 8 3 > tet 4 > 1 7 8 5 > tet 4 > 1 4 8 2 > tet 4 > 1 6 8 2 > tet 4 > 1 6 8 5 > > material 1 0 > proc_0 > 1 > 1 > 1 > 1 > 1 > 1 > > > endgmv > > 
From: Pollini Andrea <pollini@dm...>  20050107 17:06:37

On Friday 07 January 2005 15:27, KIRK, BENJAMIN (JSCEG) (NASA) wrote: > A negative Jacobian occurs when you have an overlydistorted or inverted > element. It can also be caused by having elements numbered in a > nonconsistent manner, e.g. clockwise instead of counterclockwise. > > Where did your mesh come from? If it is small, perhaps you can post it and > I can take a look? > > Hi Ben, the mesh is a cube divided into 6 tetrahedra, and I have build it by hand... after I uniformly refine it. the mesh is below... gmvinput ascii nodes 8 0 0 1 1 0 0 1 1 0 1 0 1 0 1 0 1 0 0 0 0 1 1 1 1 cells 6 tet 4 1 4 8 3 tet 4 1 7 8 3 tet 4 1 7 8 5 tet 4 1 4 8 2 tet 4 1 6 8 2 tet 4 1 6 8 5 material 1 0 proc_0 1 1 1 1 1 1 endgmv thanks in advance, Pollini Andrea 
From: Michael Schindler <mschindler@us...>  20050107 15:05:06

Hello Ben, On 07.01.05, KIRK, BENJAMIN (JSCEG) (NASA) wrote: > For example, consider Laplace's problem in 2D: > >  div(grad(u)) = 0 > > with u=g on some part of the boundary, du/dn=h on the remainder. > > In the weak statement you perform integrationbyparts, and the term du/dn > appears in a boundary integral and you can use this to impose a Neumann BC > in the RHS of the system. See, for example, > http://cfdlab.ae.utexas.edu/~benkirk/seminar/talk.pdf, Especially page 4. Do you mean just to replace du/dn in the boundary integral by h in order to "enforce" du/dn = h ?? This would be the FEM standard procedure, I guess. Exactly at this point I have some doubts. Consider a different setup, where I add the equation du/dn = h weighted with some penalty, to the linear system to be solved. This works quite well. The first prodecure is equivalent to this penaltyprocedure, if one sets the penalty to 1 which is not a really good value for a penalty. > It's not clear that you need to use the constraint matrix for this case... Therefore, I wanted to look for an alternative approach to enforce the boundary condition  and came across the constraint matrices. > For implementation, you simply need to define a finite element object that > lives on the boundary and can be used to integrate along the edge to provide > the required term. Clear? Yes, clear. For an element I would get a constraining equation (again for the case dn/du = h) h = \sum_i w_i u_i where u_i are the degrees of freedom and w_i are some weights determined by the geometry of the element. Now comes the next difficulty. I have an idea how the method DofMap::constrain_matrix_and_vector works. It creates a matrix C from the constraints and uses these constraints while inserting the correct values into the big system matrix. I would expect this _only_ to work for h = 0. Do I miss something here? > Unfortunately, none of the examples show this. If you have any more > questions let me know, it would be straightforward to modify ex14 to show > this procedure since it has the exact solution's derivative available. > Regardless, we should probably do that since it seems silly to have 14 > examples, all with Dirichlet BCs! This would be great! Thanks, Michael.  "A mathematician is a device for turning coffee into theorems" Paul Erdös. 
From: KIRK, BENJAMIN (JSCEG) (NASA) <benjamin.kirk1@na...>  20050107 14:43:34

It's not clear that you need to use the constraint matrix for this = case... For example, consider Laplace's problem in 2D: =20  div(grad(u)) =3D 0 with u=3Dg on some part of the boundary, du/dn=3Dh on the remainder. In the weak statement you perform integrationbyparts, and the term = du/dn appears in a boundary integral and you can use this to impose a Neumann = BC in the RHS of the system. See, for example, http://cfdlab.ae.utexas.edu/~benkirk/seminar/talk.pdf, Especially page = 4. In a similar way, Robin BCs can be implemented by letting h =3D alpha u = + beta du/dn. In this case you have two boundary terms that contribute to the system matrix. For implementation, you simply need to define a finite element object = that lives on the boundary and can be used to integrate along the edge to = provide the required term. Clear? Unfortunately, none of the examples show this. If you have any more questions let me know, it would be straightforward to modify ex14 to = show this procedure since it has the exact solution's derivative available. Regardless, we should probably do that since it seems silly to have 14 examples, all with Dirichlet BCs! Ben =20 Original Message From: libmeshusersadmin@... [mailto:libmeshusersadmin@...] On Behalf Of Michael Schindler Sent: Friday, January 07, 2005 3:26 AM To: libmeshusers@... Subject: [Libmeshusers] Constraint matrix for boundary conditions Hello, I would like to enforce nonDirichlet boundary conditions via the = constraint matrix. Does someone have an example how to implement this for e.g. = Neumann or Robin BC? Thanks, Michael. =20 "A mathematician is a device for turning coffee into theorems" Paul Erd=F6s.  The SF.Net email is sponsored by: Beat the postholiday blues Get a = FREE limited edition SourceForge.net tshirt from ThinkGeek. It's fun and = FREE  well, almost....http://www.thinkgeek.com/sfshirt _______________________________________________ Libmeshusers mailing list Libmeshusers@... https://lists.sourceforge.net/lists/listinfo/libmeshusers 
From: KIRK, BENJAMIN (JSCEG) (NASA) <benjamin.kirk1@na...>  20050107 14:27:05

A negative Jacobian occurs when you have an overlydistorted or inverted element. It can also be caused by having elements numbered in a nonconsistent manner, e.g. clockwise instead of counterclockwise. Where did your mesh come from? If it is small, perhaps you can post it and I can take a look? Ben Original Message From: libmeshusersadmin@... [mailto:libmeshusersadmin@...] On Behalf Of Pollini Andrea Sent: Friday, January 07, 2005 6:55 AM To: libmeshusers@... Subject: [Libmeshusers] problem with FEBase class Hi all, why when I call the method reinit in class FEBase I receive the error ERROR: negative Jacobian: 0.000244141 [0] src/fe/fe_map.C, line 405, compiled Jan 5 2005 at 11:40:52 /bin/sh: line 1: 11242 Abortito ./libmeshsteffan Press Enter to continue! thank in advance for every advice, Pollini Andrea 
From: Pollini Andrea <nelson@nu...>  20050107 12:56:48

Hi all, why when I call the method reinit in class FEBase I receive the error ERROR: negative Jacobian: 0.000244141 [0] src/fe/fe_map.C, line 405, compiled Jan 5 2005 at 11:40:52 /bin/sh: line 1: 11242 Abortito ./libmeshsteffan Press Enter to continue! thank in advance for every advice, Pollini Andrea 
From: Michael Schindler <mschindler@us...>  20050107 09:25:42

Hello, I would like to enforce nonDirichlet boundary conditions via the constraint matrix. Does someone have an example how to implement this for e.g. Neumann or Robin BC? Thanks, Michael.  "A mathematician is a device for turning coffee into theorems" Paul Erdös. 