Previously graph layout was done using the Kamada-Kawai layout algorithm

implemented in Boost.  I am replacing this with a custom implementation of
a constrained stress-majorization algorithm.

The stress-majorization algorithm is more robust and has better convergence
characteristics than Kamada-Kawai, and also simple constraints can be placed
on node position (for example, to enforce downward-pointing edges, non-overlap constraints, or cluster constraints).

Another big advantage is that we no longer need Boost.

I've tested the basic functionality, but I have yet to properly handle
disconnected graphs or to properly scale the resulting layout.

This commit also includes significant refactoring... the quadratic program solver - libvpsc (Variable Placement with Separation Constraints) has been moved to src/libvpsc and the actual graph layout algorithm is in libcola.

(bzr r1394)

1 files changed, 54 insertions, 0 deletions

diff --git a/src/libcola/cycle_detector.h b/src/libcola/cycle_detector.h
new file mode 100644
index 000000000..5cd52e324
--- /dev/null
+++ b/src/libcola/cycle_detector.h
@@ -0,0 +1,54 @@
+#ifndef CYCLE_DETECTOR_H
+#define CYCLE_DETECTOR_H
+
+#include <map>
+#include <vector>
+#include <stack>
+#include "cola.h"
+
+typedef unsigned TimeStamp;
+typedef std::vector<cola::Edge> Edges;
+typedef std::vector<bool> CyclicEdges;
+class Node;
+
+class CycleDetector  {
+  public:
+    CycleDetector(unsigned numVertices, Edges *edges);
+    ~CycleDetector();
+    std::vector<bool> *detect_cycles();
+    void mod_graph(unsigned numVertices, Edges *edges);
+    unsigned getV()  { return this->V; }
+    Edges *getEdges()  { return this->edges; }
+
+  private:
+    // attributes
+    unsigned V;
+    Edges *edges;
+
+    // internally used variables.
+    std::map<unsigned, Node *> nodes; // the nodes in the graph
+    std::map<cola::Edge, bool> cyclicEdges; // the cyclic edges in the graph.
+    std::map<unsigned, bool> traverse; // nodes still left to visit in the graph
+    std::stack<unsigned> seenInRun; // nodes visited in a single pass.
+
+    // internally used methods
+    void make_matrix();
+    void visit(unsigned k);
+    bool isSink(Node *node);
+};
+
+class Node  {
+  public:
+    enum StatusType { NotVisited, BeingVisited, DoneVisiting };
+
+    unsigned id;
+    TimeStamp stamp;
+    Node *cyclicAncestor;
+    vector<unsigned> dests;
+    StatusType status;
+
+    Node(unsigned id)  { this->id = id; cyclicAncestor = NULL; status = NotVisited; }
+    ~Node()  {}
+};
+
+#endif