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Add PR925 logic #36

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Add PR925 logic #36

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e3168cf
Add PR925 logic
AlexisOlson Sep 11, 2019
b7a741e
Add FastLogit
AlexisOlson Sep 11, 2019
9c67035
Add PR925 logic
AlexisOlson Sep 11, 2019
334f42b
Remove flag switch
AlexisOlson Sep 11, 2019
f35c4c6
Add missing bracket
AlexisOlson Sep 11, 2019
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3 changes: 2 additions & 1 deletion src/mcts/node.h
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,7 @@
#include "chess/position.h"
#include "neural/encoder.h"
#include "neural/writer.h"
#include "utils/fastmath.h"
#include "utils/mutex.h"

namespace lczero {
Expand Down Expand Up @@ -521,7 +522,7 @@ class EdgeAndNode {

int GetVisitsToReachU(float target_score, float numerator,
float default_q) const {
const auto q = GetQ(default_q);
const auto q = FastLogit(GetQ(default_q));
if (q >= target_score) return std::numeric_limits<int>::max();
const auto n1 = GetNStarted() + 1;
return std::max(
Expand Down
6 changes: 4 additions & 2 deletions src/mcts/search.cc
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Expand Up @@ -260,7 +260,8 @@ std::vector<std::string> Search::GetVerboseStats(Node* node,
<< ") ";

oss << "(Q+U: " << std::setw(8) << std::setprecision(5)
<< edge.GetQ(fpu) + edge.GetU(U_coeff) << ") ";
<< FastLogit(edge.GetQ(0)) + edge.GetU(U_coeff)
<< ") ";

oss << "(V: ";
optional<float> v;
Expand Down Expand Up @@ -1029,7 +1030,8 @@ SearchWorker::NodeToProcess SearchWorker::PickNodeToExtend(
}
}

const float score = child.GetU(puct_mult) + Q;
const float Q0 = child.GetQ(0);
const float score = child.GetU(puct_mult) + (Q - Q0) + FastLogit(0.99999999 * Q0);
if (score > best) {
second_best = best;
second_best_edge = best_edge;
Expand Down
5 changes: 5 additions & 0 deletions src/utils/fastmath.h
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Expand Up @@ -65,4 +65,9 @@ inline float FastLog(const float a) {
return 0.6931471805599453f * FastLog2(a);
}

// Fast logit for more readable code.
inline float FastLogit(const float a) {
return 0.5 * FastLog((1.0f + a) / (1.0f - a));
}

} // namespace lczero