New function pgr contraction linear

NEWS.md

@@ -42,6 +42,7 @@
 * Contraction
 
   * [#2790](https://github.com/pgRouting/pgrouting/issues/2790): pgr_contractionDeadEnd
+  * [#2791](https://github.com/pgRouting/pgrouting/issues/2791): pgr_contractionLinear
 
 ## pgRouting 3.7
 

doc/_static/page_history.js

@@ -15,7 +15,7 @@ var titles = [
 
 
 var newpages = [
-    {v: '3.8', pages: ['pgr_contractionDeadEnd']},
+    {v: '3.8', pages: ['pgr_contractionDeadEnd', 'pgr_contractionLinear']},
 
     {v: '3.7', pages: ['metrics-family', 'pgr_betweennessCentrality']},
 

doc/contraction/CMakeLists.txt

@@ -3,6 +3,7 @@ SET(LOCAL_FILES
     contraction-family.rst
     pgr_contraction.rst
     pgr_contractionDeadEnd.rst
+    pgr_contractionLinear.rst
     )
 
 foreach (f ${LOCAL_FILES})

doc/contraction/contraction-family.rst

@@ -36,6 +36,7 @@ Contraction - Family of functions
 
     pgr_contraction
     pgr_contractionDeadEnd
+    pgr_contractionLinear
 
 
 Introduction
@@ -59,173 +60,9 @@ Allowing the user to:
 - Decide the order of the contraction algorithms and set the maximum number of
   times they are to be executed.
 
-Linear contraction
--------------------------------------------------------------------------------
-In the algorithm, linear contraction is represented by 2.
-
-Linear
-................................................................................
-
-In case of an undirected graph, a node is considered a `linear` node when
-
-* The number of adjacent vertices is 2.
-
-In case of a directed graph, a node is considered a `linear` node when
-
-* The number of adjacent vertices is 2.
-* Linearity is symmetrical
-
-Linear vertex on undirected graph
-+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
-
-- The green nodes are `linear`_ nodes
-- The blue nodes have an unlimited number of incoming and outgoing edges.
-
-
-.. rubric:: Undirected
-
-.. graphviz::
-
-    graph G {
-        u, w [shape=circle;style=filled;width=.4;color=deepskyblue];
-        v [style=filled; color=green];
-        G [shape=tripleoctagon;width=1.5;style=filled;
-           color=deepskyblue;label = "Rest of the Graph"];
-
-        rankdir=LR;
-        w -- G -- u [dir=none, weight=1, penwidth=3];
-        u -- v -- w;
-    }
-
-.. list-table::
-   :width: 80
-   :widths: auto
-   :header-rows: 1
-
-   * - Node
-     - Adjacent nodes
-     - Number of adjacent nodes
-   * - :math:`v`
-     - :math:`\{u, w\}`
-     - 2
-
-Linear vertex on directed graph
-+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
-
-- The green nodes are `linear`_ nodes
-- The blue nodes have an unlimited number of incoming and outgoing edges.
-- The white node is not linear because the linearity is not symmetrical.
-
-  * It is possible to go :math:`y \rightarrow c \rightarrow z`
-  * It's not possible to go :math:`z \rightarrow c \rightarrow y`
-
-.. graphviz::
-
-    digraph G {
-        u, v, w, x, y, z [shape=circle;style=filled;width=.4;color=deepskyblue];
-        a, b [style=filled; color=green];
-        G [shape=tripleoctagon;width=1.5;style=filled;
-          color=deepskyblue;label = "Rest of the Graph"];
-
-        rankdir=LR;
-        {u, v} -> G -> {x, w, y, z} [dir=none, weight=1, penwidth=3];
-        u -> a -> v;
-        w -> b -> x;
-        x -> b -> w [color=darkgray];
-        y -> c -> z -> c;
-    }
-
-.. list-table::
-   :width: 80
-   :widths: auto
-   :header-rows: 1
-
-   * - Node
-     - Adjacent nodes
-     - Number of adjacent nodes
-     - Is symmetrical?
-   * - :math:`a`
-     - :math:`\{u, v\}`
-     - 2
-     - yes
-   * - :math:`b`
-     - :math:`\{w, x\}`
-     - 2
-     - yes
-   * - :math:`c`
-     - :math:`\{y, z\}`
-     - 2
-     - no
-
-Operation: Linear Contraction
-...............................................................................
-
-The linear contraction will stop when there are no more linear nodes.
-For example from the following graph where :math:`v` and :math:`w` are `linear`_
-nodes:
-
-.. graphviz::
-
-    digraph G {
-        u, z [shape=circle;style=filled;color=deepskyblue];
-        v, w [style=filled; color=green];
-        "G" [shape=tripleoctagon; style=filled;
-             color=deepskyblue;label = "Rest of the Graph"];
-
-        rankdir=LR;
-        G -> {u, z} [dir=none, weight=1, penwidth=3];
-        u -> v -> w -> z;
-    }
-
-Contracting :math:`w`,
-
-* The vertex :math:`w` is removed from the graph
-* The edges :math:`v \rightarrow w` and :math:`w \rightarrow z` are removed
-  from the graph.
-* A new edge :math:`v \rightarrow z` is inserted represented with red color.
-
-.. graphviz::
-
-    digraph G {
-        u, z [shape=circle;style=filled;color=deepskyblue];
-        v [style=filled; color=green];
-        "G" [shape=tripleoctagon; style=filled;
-             color=deepskyblue;label = "Rest of the Graph"];
-
-        rankdir=LR;
-        G -> {u, z} [dir=none, weight=1, penwidth=3];
-        u -> v;
-        v -> z [label="{w}";color=red]
-    }
-
-Contracting :math:`v`:
-
-* The vertex :math:`v` is removed from the graph
-* The edges :math:`u \rightarrow v` and :math:`v \rightarrow z` are removed
-  from the graph.
-* A new edge :math:`u \rightarrow z` is inserted represented with red color.
-
-
-.. graphviz::
-
-    digraph G {
-        u, z [shape=circle;style=filled;color=deepskyblue];
-        "G" [shape=tripleoctagon; style=filled;
-             color=deepskyblue;label = "Rest of the Graph"];
-
-        rankdir=LR;
-        G -> {u, z} [dir=none, weight=1, penwidth=3];
-        u -> z [label="{v, w}";color=red]
-    }
-
-Edge :math:`u \rightarrow z` has the information of nodes that were contracted.
-
-
 See Also
 -------------------------------------------------------------------------------
 
-* :doc:`pgr_contraction`
-* :doc:`sampledata`
 * https://www.cs.cmu.edu/afs/cs/academic/class/15210-f12/www/lectures/lecture16.pdf
 * https://algo2.iti.kit.edu/documents/routeplanning/geisberger_dipl.pdf
 

doc/contraction/pgr_contraction.rst

@@ -76,7 +76,7 @@ The main Characteristics are:
   function:
 
   - Dead End Contraction. See :doc:`pgr_contractionDeadEnd`.
-  - Linear Contraction. See :doc:`contraction-family`.
+  - Linear Contraction. See :doc:`pgr_contractionLinear`.
 
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