+/*---------- combined vertex displacement ----------*/
+
+ /*
+ * At vertex Q considering edge direction e to R
+ * and corresponding opposite edge to P.
+ *
+ * Let R' = Q + PQ
+ * D = R' - R
+ * delta
+ * [ -1 ]
+ * cost = [ lambda . ( D . PQ/|PQ| ) + | D x PQ/|PQ| | ]
+ * Q,e [ ------------------------------------------- ]
+ * [ |PQ| ]
+ */
+
+double vertex_displacement_cost(const Vertices vertices, int section) {
+ const double inv_lambda= 1.0/1; //2;
+ const double delta= 4;
+ const double pqlen2_epsilon= 1e-12;
+
+ int pi,e,qi,ri, k;
+ double pq[D3], d[D3], ddot, dcross[D3];
+ double total_cost= 0;
+
+ FOR_EDGE(qi,e,ri, OUTER) {
+ pi= EDGE_END2(qi,(e+3)%V6); if (pi<0) continue;
+
+ K pq[k]= -vertices[pi][k] + vertices[qi][k];
+ K d[k]= vertices[qi][k] + pq[k] - vertices[ri][k];
+ ddot= dotprod(d,pq);
+ xprod(dcross, d,pq);
+ double pqlen2= magnD2(pq);
+ double cost_basis= inv_lambda * ddot + magnD(dcross);
+ double cost= pow(cost_basis / (pqlen2 + pqlen2_epsilon), delta);
+
+ total_cost += cost;
+ }
+ return total_cost;
+}
+
+/*---------- at-vertex edge angles ----------*/