# matrix in OpenFOAM

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 August 23, 2013, 09:51 matrix in OpenFOAM #1 Member   Hassan Join Date: Oct 2012 Location: Iran Posts: 63 Rep Power: 6 Hello all, According to the reference that it's address link is below, in page 53; http://www.diva-portal.org/smash/get...T01.pdf‎ I can,t undrestand that what is the placeholder matrix in openFoam? and how get this equations: u(0)=[2,0] u(1)=[3,1] l(0)=[0,2] l(1)=[1,3] UpperAddr=(2,3) LowerAddr=(0,1) Best regards, Hassan

 August 26, 2013, 01:36 #2 Member   Hassan Join Date: Oct 2012 Location: Iran Posts: 63 Rep Power: 6 can anyone explain the placeholder matrix in openfoam?

 August 27, 2013, 03:47 #3 New Member   Amin Join Date: Dec 2012 Posts: 2 Rep Power: 0 Dear Hassan, As far as I know, OF uses a LDU method to store large sparse matrixes to save memory. In your reference, A is a matrix which is stored as the sum of three matrixes. 1- Diagonal list which stores only diagonal elements. 2- Lower list for storing lower triangular elements, row wised from left to right. 3- Upper list for storing upper triangular elements, column wised from left to right. Then for addressing these off-diagonal elements, since upper and lower elements are symmetric, only one of them are addressed. E.g. upperAddr contains the rows of lower list elements and lowerAddr contains the column of them. So for upper list elements, upperAddr is for columns and lowerAddr is for rows. Regards, Amin sina.s, hua1015, sharonyue and 2 others like this. Last edited by Amiin; August 29, 2013 at 07:37.

 August 29, 2013, 14:32 #4 Member   Hassan Join Date: Oct 2012 Location: Iran Posts: 63 Rep Power: 6 Dear Amin, thanks a lot Best regadrs, Hassan

 August 31, 2013, 00:43 #5 Member   Hassan Join Date: Oct 2012 Location: Iran Posts: 63 Rep Power: 6 Hi, According to the: http://openfoamwiki.net/index.php/Op...es_in_OpenFOAM What is the "computational molecule" term in the Sentence below? "OpenFOAM uses a small computational molecule, therefore only adjacent cells influence one another." Best regards, Hassan

 September 2, 2013, 02:45 #6 Senior Member   Dongyue Li Join Date: Jun 2012 Location: Torino, Italy Posts: 751 Rep Power: 10 Hi guys: If the solver prints: Code: ```Lower triangle = 7(-0.05 -0 -0.05 -0 -0 -0.05 -0.05) diagonal = 6(0.05 0.05 0 0.05 0.05 0) Upper triangle = 7{0}``` what does it mean? if the diagonal coefficients are 6, is the upper and lower triangle coefficients should be (5+4+3+2+1)=15?

 September 9, 2013, 14:27 #7 Member   Hassan Join Date: Oct 2012 Location: Iran Posts: 63 Rep Power: 6 good question, I don't know!

 September 9, 2013, 18:11 #8 Member   Join Date: Nov 2012 Posts: 71 Rep Power: 6 if the matrix is symmetric, only the diagonal is stored to save RAM. can be seen in the ldumatrix class

 September 16, 2013, 02:04 #9 Member   Hassan Join Date: Oct 2012 Location: Iran Posts: 63 Rep Power: 6 Hi sharonyue, How can get this output? access to the these lists in a special test case for example in cavity by icoFoam: Code: ```Lower triangle = 7(-0.05 -0 -0.05 -0 -0 -0.05 -0.05) diagonal = 6(0.05 0.05 0 0.05 0.05 0) Upper triangle = 7{0}``` Regards, Hassan

 February 1, 2014, 13:00 #10 Member   Avdeev Evgeniy Join Date: Jan 2011 Location: Togliatty, Russia Posts: 61 Blog Entries: 1 Rep Power: 14 Hello, luckycfd. Probably matricoFoam will help you to understand: http://www.cfd-online.com/Forums/ope...tml#post472905 wyldckat and luckycfd like this.

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