new energy calculation but anarres crashes

[moebius2.git] / graph.c

diff --git a/graph.c b/graph.c
new file mode 100644 (file)
index 0000000..c9cdd2c
--- /dev/null
+++ b/graph.c
@@ -0,0 +1,116 @@
+/*
+ * graph layout energy
+ */
+
+#include "mgraph.h"
+#include "minimise.h"
+
+static int sqdistances[N][N];
+
+static double alpha, beta, beta_prime;
+
+static void breadth_first_search(int start, int sqdistances_r[N]) {
+  int d[N], buffer[N], *buf_pop=buffer, *buf_push=buffer;
+  int v,e, current, future, dfuture;
+
+  buf_push= buf_pop= buffer;
+  FOR_VERTEX(v) d[v]= -1;
+
+  d[start]= 0;
+  *buf_push++= start;
+
+  while (buf_pop < buf_push) {
+    current= *buf_pop++;
+    dfuture= d[current] + 1;
+    FOR_VEDGE(current,e,future) {
+      if (d[future] >= 0) continue; /* already found this one */
+      d[future]= dfuture;
+      *buf_push++= future;
+    }
+  }
+  assert(buf_pop==buf_push);
+  assert(buf_push <= buffer+sizeof(buffer)/sizeof(buffer[0]));
+
+  FOR_VERTEX(v) {
+    assert(d[v] >= 0);
+    sqdistances_r[v]= d[v] * d[v];
+  }
+}
+
+void graph_layout_prepare() {
+  int v1;
+  
+  FOR_VERTEX(v1)
+    breadth_first_search(v1, sqdistances[v1]);
+
+  alpha= 2;
+  beta= -log(10)/log(alpha);
+  beta_prime= (1-beta)/2;
+  printf("alpha=%g beta=%g beta'=%g\n", alpha,beta,beta_prime);
+}
+
+
+double graph_layout_cost(const Vertices v, const double vertex_areas[N]) {
+  /* For each (vi,vj) computes shortest path s_ij = |vi..vj|
+   * along edges, and actual distance d_ij = |vi-vj|.
+   *
+   * We will also use the `vertex areas': for each vertex vi the
+   * vertex area a_vi is the mean area of the incident triangles.
+   * This is computed elsewhere.
+   *
+   * Energy contribution is proportional to
+   *
+   *               -4          2
+   *    a  a   .  d   . [ (s/d)  - 1 ]
+   *     vi vj
+   *
+   * (In practice we compute d^2+epsilon and use it for the
+   *  divisions, to avoid division by zero.)
+   */
+  //static const double d2_epsilon= 1e-6;
+
+  //  double edge_weights[V6<<ESHIFT], vertex_distances[N],
+  double total_cost=0;
+  int v1,v2,e, nedges=0;
+  double totaledgelength=0, meanedgelength, meanedgelength2;
+
+  FOR_EDGE(v1,e,v2) {
+    totaledgelength += hypotD(v[v1], v[v2]);
+    nedges++;
+  }
+
+  meanedgelength= totaledgelength / nedges;
+  meanedgelength2= meanedgelength * meanedgelength;
+//  printf("mean=%g mean^2=%g\n", meanedgelength, meanedgelength2);
+    
+  FOR_VERTEX(v1) {
+    FOR_VERTEX(v2) {
+      if (v1 == v2) continue;
+
+      double d2= hypotD2(v[v1],v[v2]);
+      
+      int dist2= sqdistances[v1][v2];
+      assert(dist2>0);
+
+      double s2= dist2 * meanedgelength2;
+
+      /* energy = (d/s)^(1-beta)     where beta is -log\_{alpha}(10)
+       * energy = ((d/s)^2) ^ (1-beta)/2
+       *          let beta' = (1-beta)/2
+       */
+
+      double cost= pow(d2/s2, beta_prime);
+      
+      //double s2= s*s + d2_epsilon;
+      //double sd2= s2 / d2;
+      //double cost_contrib= a1*a2 * (sd2 - 1) / (d2*d2);
+      //double cost_contrib= sd2;
+
+      //printf("layout %03x..%03x dist^2=%d s^2=%g d^2=%g "
+              //" cost+=%g\n", v1,v2, dist2,
+              //            s2,d2, cost);
+      total_cost += cost;
+    }
+  }
+  return total_cost;
+}