On 3/27/19 2:52 AM, Phạm Ngọc Kiên wrote: > > My question for assembling the system is > when I set the cell right hand side is none zero at a given dofs (source > dofs), should I assemble the cell matrix at these dofs none zeros? > Should both cell matrix (i,j) and cell right hand side (i) be zeros for the > dofs i , j which are not at the source dof?
I don't think we quite understood what you are doing. Let's say your right hand side function is J(x), then the right hand side vector should be F_i = \int_\Omega \phi_i(x) J(x) dx I *think* what you are describing is that your J(x) is actually a delta function at a single point, which you call the "source dof". If that is the case, say that J(x) is a delta function located at x0, then you need to compute F_i = \phi_i(x0) which may or may not be equal to one -- in any case, making the assumption that a shape function has a particular value at a particular point is a bad idea, and the right approach is to evaluate it at that point to get its value. It is worth pointing out that while the description of source located at individual points is often used, it is not a physically correct description. No sources are point sources. A physically correct description would use distributed sources (which leads to integrals that are not approximated by point values), and as you are discovering, using the "simplification" of describing sources as point sources actually makes all sorts of things more complicated in finite element codes. Does this make sense? Best W. -- ------------------------------------------------------------------------ Wolfgang Bangerth email: [email protected] www: http://www.math.colostate.edu/~bangerth/ -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
