Update some missing Lagrange docs

[termi-official]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.60%. Comparing base (baf8aad) to head (4437a85).

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@@           Coverage Diff           @@
##           master     #889   +/-   ##
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  Coverage   93.60%   93.60%           
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  Files          39       39           
  Lines        5879     5883    +4     
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+ Hits         5503     5507    +4     
  Misses        376      376           

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[KnutAM]

Nice!
Just some formatting fix suggestions while we are at it...

[termi-official]

I noticed that on master some things can be now done in a better way (i.e. without relying on assumptions taken between the interpolation and cell) so I updated it. Also some dispatches were missing, which I added for completeness of the API.

[termi-official]

I just saw that #935 has quite a bit of overlap here, so we need to decide on a merge order.

[termi-official]

CI failure seems to be the github CDN or CI servers choking

ERROR: LoadError: LoadError: LoadError: Operation too slow. Less than 1 bytes/sec transferred the last 20 seconds while requesting https://raw.githubusercontent.com/Ferrite-FEM/Ferrite.jl/gh-pages/assets/transient_heat.gif

[KnutAM]

LGTM if if removing changes in grid.md as discussed on Slack, and fixes the comments

[termi-official]

Example to be reinserted separately.

Now to a full example. Let us reconstruct the local facets of a grid boundary with the described machinery to see how everything
fits together:

julia> function recompute_facetset_on_boundary(cells, global_facets)
           # Facets in 2D are edges and have two vertices
           d = Dict{NTuple{2, Int}, FacetIndex}()
           for (c, cell) in enumerate(cells) # c is global cell number
               # Grab all local facets
               local_facets = Ferrite.reference_facets(cell)
               for (f, facet) in enumerate(local_facets) # f is local facet number
                   # Translate into global nodes
                   global_facet = ntuple(i-> cell.nodes[facet[i]], length(facet))
                   d[global_facet] = FacetIndex(c, f)
               end
           end

           facets = Vector{FacetIndex}()
           for facet in global_facets
               # lookup the element, local facet combination for this facet
               push!(facets, d[facet])
           end

           return facets
       end

julia> recompute_facetset_on_boundary(cells, facets)
Vector{FacetIndex} with 2 elements:
  FacetIndex((2, 2))
  FacetIndex((4, 2))

Note that this example can be simplified by directly using Ferrite.facets:

julia> function recompute_facetset_on_boundary_alternative(cells, global_facets)
           # Facets in 2D are edges and have two vertices
           d = Dict{NTuple{2, Int}, FacetIndex}()
           for (c, cell) in enumerate(cells) # c is global cell number
               # Grab all local facets
               for (f, global_facet) in enumerate(Ferrite.facets(cell)) # f is local facet number
                   d[global_facet] = FacetIndex(c, f)
               end
           end

           facets = Vector{FacetIndex}()
           for facet in global_facets
               # lookup the element, local facet combination for this facet
               push!(facets, d[facet])
           end

           return facets
       end

julia> recompute_facetset_on_boundary_alternative(cells, facets)
Vector{FacetIndex} with 2 elements:
  FacetIndex((2, 2))
  FacetIndex((4, 2))

[KnutAM]

Spotted a few more things when going through carefully

[KnutAM]

Nice!

A lot of discussion for a small docs PR :)
But I think we ended up with some quite important improvements / clarifications in the end!