// Here is a formula for the area of a polygon with vertices {(xk,yk): k = 1,...,n}:
// Area = 1/2 [(x1*y2 - x2*y1) + (x2*y3 - x3*y2) + ... + (xn*y1 - x1*yn)].
// This formula appears in an Article by Gil Strang of MIT
// on p. 253 of the March 1993 issue of The American Mathematical Monthly, with the note that it
// is
// "known, but not well known". There is also a very brief discussion of proofs and other
// references,
// including an article by Bart Braden of Northern Kentucky U., a known Mathematica enthusiast.
public double calculateArea() {
// rescaleToPositiveCoordinates();
double area = 0;
// we can implement it like this because the polygon is closed (point2D.get(0) =
// point2D.get(length + 1)
for (int i = 0; i < length; i++) {
area += (x[i] * y[i + 1] - x[i + 1] * y[i]);
}
return (Math.abs(area / 2));
}
public void proposeTree() throws OperatorFailedException {
TreeModel tree = c2cLikelihood.getTreeModel();
BranchMapModel branchMap = c2cLikelihood.getBranchMap();
NodeRef i;
double oldMinAge, newMinAge, newRange, oldRange, newAge, q;
// choose a random node avoiding root, and nodes that are ineligible for this move because they
// have nowhere to
// go
final int nodeCount = tree.getNodeCount();
do {
i = tree.getNode(MathUtils.nextInt(nodeCount));
} while (tree.getRoot() == i || !eligibleForMove(i, tree, branchMap));
final NodeRef iP = tree.getParent(i);
// this one can go anywhere
NodeRef j = tree.getNode(MathUtils.nextInt(tree.getNodeCount()));
NodeRef k = tree.getParent(j);
while ((k != null && tree.getNodeHeight(k) <= tree.getNodeHeight(i)) || (i == j)) {
j = tree.getNode(MathUtils.nextInt(tree.getNodeCount()));
k = tree.getParent(j);
}
if (iP == tree.getRoot() || j == tree.getRoot()) {
throw new OperatorFailedException("Root changes not allowed!");
}
if (k == iP || j == iP || k == i) throw new OperatorFailedException("move failed");
final NodeRef CiP = getOtherChild(tree, iP, i);
NodeRef PiP = tree.getParent(iP);
newMinAge = Math.max(tree.getNodeHeight(i), tree.getNodeHeight(j));
newRange = tree.getNodeHeight(k) - newMinAge;
newAge = newMinAge + (MathUtils.nextDouble() * newRange);
oldMinAge = Math.max(tree.getNodeHeight(i), tree.getNodeHeight(CiP));
oldRange = tree.getNodeHeight(PiP) - oldMinAge;
q = newRange / Math.abs(oldRange);
// need to account for the random repainting of iP
if (branchMap.get(PiP.getNumber()) != branchMap.get(CiP.getNumber())) {
q *= 0.5;
}
if (branchMap.get(k.getNumber()) != branchMap.get(j.getNumber())) {
q *= 2;
}
tree.beginTreeEdit();
if (j == tree.getRoot()) {
// 1. remove edges <iP, CiP>
tree.removeChild(iP, CiP);
tree.removeChild(PiP, iP);
// 2. add edges <k, iP>, <iP, j>, <PiP, CiP>
tree.addChild(iP, j);
tree.addChild(PiP, CiP);
// iP is the new root
tree.setRoot(iP);
} else if (iP == tree.getRoot()) {
// 1. remove edges <k, j>, <iP, CiP>, <PiP, iP>
tree.removeChild(k, j);
tree.removeChild(iP, CiP);
// 2. add edges <k, iP>, <iP, j>, <PiP, CiP>
tree.addChild(iP, j);
tree.addChild(k, iP);
// CiP is the new root
tree.setRoot(CiP);
} else {
// 1. remove edges <k, j>, <iP, CiP>, <PiP, iP>
tree.removeChild(k, j);
tree.removeChild(iP, CiP);
tree.removeChild(PiP, iP);
// 2. add edges <k, iP>, <iP, j>, <PiP, CiP>
tree.addChild(iP, j);
tree.addChild(k, iP);
tree.addChild(PiP, CiP);
}
tree.setNodeHeight(iP, newAge);
tree.endTreeEdit();
//
logq = Math.log(q);
// repaint the parent to match either its new parent or its new child (50% chance of each).
if (MathUtils.nextInt(2) == 0) {
branchMap.set(iP.getNumber(), branchMap.get(k.getNumber()), true);
} else {
branchMap.set(iP.getNumber(), branchMap.get(j.getNumber()), true);
}
if (DEBUG) {
c2cLikelihood.checkPartitions();
}
}