/**
* Builds a ball tree middle out from the portion of the master index array given by supplied
* start and end index.
*
* @param startIdx The start of the portion in master index array.
* @param endIdx the end of the portion in master index array.
* @return The root node of the built tree.
* @throws Exception If there is some problem building the tree.
*/
protected BallNode buildTreeMiddleOut(int startIdx, int endIdx) throws Exception {
Instance pivot;
double radius;
Vector<TempNode> anchors;
int numInsts = endIdx - startIdx + 1;
int numAnchors = (int) Math.round(Math.sqrt(numInsts));
// create anchor's hierarchy
if (numAnchors > 1) {
pivot = BallNode.calcCentroidPivot(startIdx, endIdx, m_InstList, m_Instances);
radius =
BallNode.calcRadius(startIdx, endIdx, m_InstList, m_Instances, pivot, m_DistanceFunction);
if (numInsts <= m_MaxInstancesInLeaf
|| (rootRadius == 0
? true
: radius / rootRadius
< m_MaxRelLeafRadius)) { // just make a leaf don't make anchors hierarchy
BallNode node = new BallNode(startIdx, endIdx, m_NumNodes, pivot, radius);
return node;
}
anchors = new Vector<TempNode>(numAnchors);
createAnchorsHierarchy(anchors, numAnchors, startIdx, endIdx);
BallNode node = mergeNodes(anchors, startIdx, endIdx);
buildLeavesMiddleOut(node);
return node;
} // end anchors hierarchy
else {
BallNode node =
new BallNode(
startIdx,
endIdx,
m_NumNodes,
(pivot = BallNode.calcCentroidPivot(startIdx, endIdx, m_InstList, m_Instances)),
BallNode.calcRadius(
startIdx, endIdx, m_InstList, m_Instances, pivot, m_DistanceFunction));
return node;
}
}
/**
* Builds a ball tree middle out.
*
* @return The root node of the tree.
* @throws Exception If there is problem building the tree.
*/
public BallNode buildTree() throws Exception {
m_NumNodes = m_MaxDepth = m_NumLeaves = 0;
if (rootRadius == -1) {
rootRadius =
BallNode.calcRadius(
m_InstList,
m_Instances,
BallNode.calcCentroidPivot(m_InstList, m_Instances),
m_DistanceFunction);
}
BallNode root = buildTreeMiddleOut(0, m_Instances.numInstances() - 1);
return root;
}
/**
* Returns an anchor point which is furthest from the mean point for a given set of points
* (instances) (The anchor instance is chosen from the given set of points).
*
* @param startIdx The start index of the points for which anchor point is required.
* @param endIdx The end index of the points for which anchor point is required.
* @return The furthest point/instance from the mean of given set of points.
*/
protected TempNode getFurthestFromMeanAnchor(int startIdx, int endIdx) {
TempNode anchor = new TempNode();
Instance centroid = BallNode.calcCentroidPivot(startIdx, endIdx, m_InstList, m_Instances);
Instance temp;
double tmpr;
anchor.radius = Double.NEGATIVE_INFINITY;
for (int i = startIdx; i <= endIdx; i++) {
temp = m_Instances.instance(m_InstList[i]);
tmpr = m_DistanceFunction.distance(centroid, temp);
if (tmpr > anchor.radius) {
anchor.idx = m_InstList[i];
anchor.anchor = temp;
anchor.radius = tmpr;
}
}
setPoints(anchor, startIdx, endIdx, m_InstList);
return anchor;
}
