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- - **The meanings of diag( ), source( ), psi( )**
(*https://www.cfd-online.com/Forums/openfoam-programming-development/86170-meanings-diag-source-psi.html*)

The meanings of diag( ), source( ), psi( )I am using the solver"porousSimpleFoam" to run simulations on a domain including porous media.
In the UEqn.H, the momentum equation is implemented as follows: // Construct the Momentum equation tmp<fvVectorMatrix> UEqn ( fvm::div(phi, U) + turbulence->divDevReff(U) ); Then in the file: /src/finiteVolume/cfdTools/general/porousMedia/porousZone.C we have the following code: ================================================== ========== scalarField& Udiag = UEqn.diag();vectorField& Usource = UEqn.source();const vectorField& U = UEqn.psi();================================================== ========== Does anyone know the exact meanings of UEqn.diag(), UEqn.source(), UEqn.psi() in details, e.g. what do these functions return? Or could anyone give some hints about that?Thank you very much |

See the source code documentation.
Here is the list of all members of fvMatrix since diag() is inheirited http://foam.sourceforge.net/docs/cpp...ix-members.php |

Hi,
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UEqn.diag(); gives you the diagonal of system matrix, UEqn.source(); the source term (both without applying BC's) and UEqn.psi(); a reference to the unknown field. Remember that UEqn is the whole linear system not only the matrix.Regards. |

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Hi Santiago. Thanks for your reply. In the openfoamwiki, I learn that disretization of PDE leads to an algebraic equation in the following form: AΨ = BSo does UEqn.diag() mean the diagonal of A, UEqn.source() mean B and UEqn.psi() mean Ψ ? |

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Please attention to this post. ? Regards, Hassan |

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For example, if you are discritizing velocity, u will have an symmetry matrix. After discritization, u will have Ax = B, A will be symmetric, Then OpenFOAM will do: [A.diag()+A.offdiag()] x = B; A.diag() x = B - A.offdiag() x; For symmetric matrix, A.diag() will be the diagonal of A, A.offdiag() x will be the source of A. That means if your matrix equation is like this: A x = 0; U also have an source() term. :) |

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