# NetworkSimplex Dead Fields

**URL:** <https://forum.graphviz.org/t/networksimplex-dead-fields/3045>\
**Category:** Dev\
**Created:** [June 24, 2025, 5:04pm UTC](https://forum.graphviz.org/t/networksimplex-dead-fields/3045 "2025-06-24T17:04:08Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Chr15W3](https://avatars.discourse-cdn.com/v4/letter/c/a5b964/32.png) [@Chr15W3](https://forum.graphviz.org/u/Chr15W3)\
**Post date:** [June 24, 2025, 5:04pm UTC](https://forum.graphviz.org/t/networksimplex-dead-fields/3045/1 "2025-06-24T17:04:08Z")

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Hi all!  
I’m currently trying to properly understand the C NetworkSimplex implementation in `ns.c` and have some trouble understanding some of the fields. In particular, I am wondering if (and what) the field `network_simplex_ctx_t->Tree_node` does. It is opulated during the subtree search, in the `add_tree_edge` function, however, I cannot find any later use of this. The only other read/write reference as far as i can tell is in the `TB_Balance` function, but there it is always overwritten from the beginning

Thanks for helping me understand this!

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**Author:** ![scnorth](https://sea2.discourse-cdn.com/graphviz/user_avatar/forum.graphviz.org/scnorth/32/89_2.png) [@scnorth](https://forum.graphviz.org/u/scnorth)\
**Post date:** [June 26, 2025, 1:43pm UTC](https://forum.graphviz.org/t/networksimplex-dead-fields/3045/2 "2025-06-26T13:43:54Z")

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It doesn’t seem important. This list is also referenced in a debugging function `tchk()` (“tree check”) that was mostly helpful back when we first wrote and debugged this code.

If you can understand how the solver finds an initial feasible solution, then iteratively improves it by restructuring the “tight tree” by swapping tree edges based on cut values, you have the important details.

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<div class="post-metadata">

**Author:** ![smattr](https://sea2.discourse-cdn.com/graphviz/user_avatar/forum.graphviz.org/smattr/32/85_2.png) [@smattr](https://forum.graphviz.org/u/smattr)\
**Post date:** [July 1, 2025, 10:41am UTC](https://forum.graphviz.org/t/networksimplex-dead-fields/3045/3 "2025-07-01T10:41:39Z")

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> **[common: demote 'Tree\_node' to a local of 'TB\_balance' (!4418) · Merge requests...](https://gitlab.com/graphviz/graphviz/-/merge_requests/4418)**
>
> It seems to have gone unnoticed in