I'll be happy to keep CC'ing the mailing list, sorry, my finger slipped! I'm afraid I didn't see your extended advice until just now.
While I do want to search for other points contained within a horizon about a given point, I was mistaken before, and this procedure actually has little to do with the large tolerance I was setting (if I understand correctly) Thanks for your comment on efficiency. I'll look into these alternative methods. I actually just want to, given a physical point, get the value of the shape functions at that point. Should I proceed as I am, or would it make more sense to use something like http://libmesh.github.io/examples/miscellaneous_ex8.html to interpolate the values of the shape functions over the mesh? This would introduce additional interpolation error, though? On Thu, Nov 16, 2017 at 11:25 AM, Roy Stogner <[email protected]> wrote: > > Oh, and now that I've noticed: please keep Cc:ing the mailing list; > the more helpful discussion that gets archived where future users' > search engines can find it, the better. > > Thanks, > --- > Roy > > > On Thu, 16 Nov 2017, Roy Stogner wrote: > > >> On Wed, 15 Nov 2017, Zack Vitoh wrote: >> >> Pure virtual functions (like those found in the PointLocatorBase and >>> related classes) were completely new to me earlier today, but I believe I >>> understand the proper syntax, at least, so if it's of use to anyone >>> else, here is an example of one way to use the PointLocatorBase class (to >>> find >>> the element 'elem_ploc' containing (0,-0.5,0)) >>> >>> UniquePtr<PointLocatorBase> >>> my_point_locator(PointLocatorBase::build(TREE_ELEMENTS, >>> mesh)); >>> >> >> This should work, but it's not the most efficient way to go: >> although PointLocatorTree::operator() is O(log N), >> PointLocatorTree::build() is O(N), so you only get a fast amortized >> lookup if you can reuse the same point locator over and over again. >> >> Try >> >> UniquePtr<PointLocatorBase> my_point_locator = mesh.sub_point_locator(); >> >> That will create a sub-locator which reuses the same main locator >> instead of building a new one each time. >> >> Real mpl_tol = 2.0 * diam; >>> my_point_locator->set_close_to_point_tol (mpl_tol); >>> my_point_locator->enable_out_of_mesh_mode(); >>> >> >> I assume diam is an element diameter? Then you're trying to find >> points as far as two diameters away from any current element? I'm >> afraid that's not guaranteed to work - if you have quads or other >> non-affine elements in your mesh, you can have mapping functions which >> are invertible on the elements (so the mesh is perfectly valid) but >> which become singular far away from the elements (so the >> transformations we do when checking whether an element contains a >> point become invalid). Beware. >> >> Also, with a huge tolerance, you are going to have multiple elements >> which "contain" a point, and the point locator may not return an >> element which *actually* contains the point, even if one exists, if it >> finds a merely close by element first. >> >> const Elem* elem_ploc = my_point_locator->operator()( >>> Point(0.,-0.5,0.) ); >>> >> >> For operator(), terser syntax is: >> >> const Elem* elem_ploc = (*my_point_locator)( Point(0.,-0.5,0.) ); >> >> Knowing the full ugly syntax is still useful, unfortunately, for >> debugging with gdb... >> --- >> Roy > > ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
