bool BVH4BuilderFast::splitSequential(BuildRecord& current, BuildRecord& leftChild, BuildRecord& rightChild)
{
/* mark as leaf if leaf threshold reached */
if (current.items() <= QBVH_BUILDER_LEAF_ITEM_THRESHOLD) {
current.createLeaf();
return false;
}
/* calculate binning function */
Mapping<16> mapping(current.bounds);
/* binning of centroids */
Binner<16> binner;
binner.bin(prims,current.begin,current.end,mapping);
/* find best split */
Split split;
binner.best(split,mapping);
/* if we cannot find a valid split, enforce an arbitrary split */
if (unlikely(split.pos == -1)) split_fallback(prims,current,leftChild,rightChild);
/* partitioning of items */
else binner.partition(prims, current.begin, current.end, split, mapping, leftChild, rightChild);
if (leftChild.items() <= QBVH_BUILDER_LEAF_ITEM_THRESHOLD) leftChild.createLeaf();
if (rightChild.items() <= QBVH_BUILDER_LEAF_ITEM_THRESHOLD) rightChild.createLeaf();
return true;
}
std::vector<int> count(Binner binner) {
std::vector<int> out;
int n = binner.size();
for(int i = 0; i < n; ++i) {
int bin = binner.bin(i);
if (bin < 0) continue;
// Make sure there's enough space
if (bin >= out.size()) {
out.resize(bin + 1);
}
++out[bin];
}
return out;
}
std::vector<double> CanonicalAverager::calculate_weights(const std::vector<double> &energies, const Binner &binner, const DArray &lnG, const BArray &lnG_support, double beta) {
// Assert the arrays got same shape and are one dimensional
assert(lnG.same_shape(lnG_support));
assert(lnG.get_shape().size()==1);
unsigned int nbins = lnG.get_shape(0);
// First make a histogram of the energies given as argument
UArray histogram(nbins);
for(std::vector<double>::const_iterator it=energies.begin(); it < energies.end(); it++) {
int bin = binner.calc_bin(*it);
if (0 <= bin && bin < static_cast<int>(nbins)) {
histogram(bin)++;
}
}
// Calculate the support for this histogram
BArray histogram_support = histogram > 0;
// Calculate the normalization constant for the canonical distribution,
// by summing over the area with both the histogram and the estimated
// entropy (lnG) has support. The normalization constant is given by
//
// lnZ_beta = log(Z_beta) = log[ sum_E exp( S(E) - beta*E ) ]
//
// To calculate this we use the log-sum-exp trick
BArray support = histogram_support && lnG_support;
DArray binning = binner.get_binning_centered();
DArray summands(nbins);
for (BArray::constwheretrueiterator it = support.get_constwheretrueiterator(); it(); ++it) {
summands(it) = lnG(it) - beta*binning(it);
}
double lnZ_beta = log_sum_exp(summands, support);
// Now calculate the probability for each bin according to the canonical ensemble
DArray P_beta(nbins);
for (BArray::constwheretrueiterator it = support.get_constwheretrueiterator(); it(); ++it) {
P_beta(it) = exp(-beta*binning(it) + lnG(it) - lnZ_beta);
}
// Calculate the weight for each energy in the energy vector
std::vector<double> weights;
for(std::vector<double>::const_iterator it=energies.begin(); it < energies.end(); it++) {
int bin = binner.calc_bin(*it);
if (0 <= bin && bin < static_cast<int>(nbins)) {
double weight = 1.0/static_cast<double>(histogram(bin)) * P_beta(bin);
weights.push_back(weight);
}
else {
weights.push_back(0);
}
}
return weights;
}
