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Commit bab4617e authored by Christophe Geuzaine's avatar Christophe Geuzaine
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explain impact of non-continuous node/element tags

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...@@ -3249,6 +3249,16 @@ before the @code{$Elements} section. Currently only one @code{$Nodes} ...@@ -3249,6 +3249,16 @@ before the @code{$Elements} section. Currently only one @code{$Nodes}
and one @code{$Elements} section are allowed per file. (This might/will and one @code{$Elements} section are allowed per file. (This might/will
change in the future.) change in the future.)
Important note about efficiency. Node and element tags can be "sparse",
i.e., do not have to constitute a continuous list of indexes starting at
1. However, using non-continuous tags will lead to performance
degradation. For meshes, non-continuous indexing forces Gmsh to use a
map instead of a vector to access nodes and elements. The performance
hit is on speed. For post-processing datasets, which always use vectors
to access data, the performance hit is on memory. A @code{NodeData} with
two nodes, tagged 1 and 1000000, will allocate a (mostly empty) vector
of 1000001 elements.
Any section with an unrecognized header is simply ignored: you can thus Any section with an unrecognized header is simply ignored: you can thus
add comments in a @file{.msh} file by putting them e.g. inside a add comments in a @file{.msh} file by putting them e.g. inside a
@code{$Comments}/@code{$EndComments} section. @code{$Comments}/@code{$EndComments} section.
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