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Change mlh threshold effect to create a smooth transition #1844

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merged 8 commits into from
May 21, 2023
Merged

Change mlh threshold effect to create a smooth transition #1844

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fb3b031
changed threshold effect to create a smooth transition
Naphthalin Feb 10, 2023
d51267b
Merge branch 'master' into soft-mlh
Naphthalin Mar 28, 2023
ccf212f
Merge branch 'master' into soft-mlh
Naphthalin Apr 15, 2023
2832267
Merge branch 'master' into soft-mlh
Naphthalin Apr 23, 2023
4a24371
Merge branch 'master' into soft-mlh
Naphthalin May 4, 2023
cc07b4e
renamed GetM() to GetMUtility() to differentiate it from GetM()
Naphthalin May 6, 2023
2debd43
added comment
Naphthalin May 6, 2023
79f0a06
changed duplicate GetMUtility() function into wrapper
Naphthalin May 8, 2023
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40 changes: 23 additions & 17 deletions src/mcts/search.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -106,26 +106,29 @@ class MEvaluator {
}
}

float GetM(const EdgeAndNode& child, float q) const {
// Calculates the utility for favoring shorter wins and longer losses.
float GetMUtility(Node* child, float q) const {
if (!enabled_ || !parent_within_threshold_) return 0.0f;
const float child_m = child.GetM(parent_m_);
const float child_m = child->GetM();
float m = std::clamp(m_slope_ * (child_m - parent_m_), -m_cap_, m_cap_);
m *= FastSign(-q);
if (q_threshold_ > 0.0f && q_threshold_ < 1.0f) {
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Could you add a comment what GetM function does?

I though it returns moves left, but then it returns 0 if |q| < q_thredshol, so it's not clear what it's supposed to do.

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It returns the "moves left head effect" term which gets added to the PUCT score, so that PUCT = Q + U + M. This PR doesn't change the meaning of GetM(), but your comment makes clear that it was already confusing before this PR, so a comment (even if it has nothing to do with this PR) would certainly justified.

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Something like this before the function declaration.

// Returns adjustment to Q based on Q and M value of a node.

Could you add this in this PR?

Also, GetM() sounds like a wrong name for this function. Maybe rename to GetQAdjustment() ?
(it's more or less clear that it's based on M because it inside the MEvaluator class).

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Settled at GetMUtility() because it best describes both where it comes from (M) and what it is (a utility).

// This allows a smooth M effect with higher q thresholds, which is
// necessary for using MLH together with contempt.
q = std::max(0.0f, (std::abs(q) - q_threshold_)) / (1.0f - q_threshold_);
}
m *= a_constant_ + a_linear_ * std::abs(q) + a_square_ * q * q;
return m;
}

float GetM(Node* child, float q) const {
float GetMUtility(const EdgeAndNode& child, float q) const {
if (!enabled_ || !parent_within_threshold_) return 0.0f;
const float child_m = child->GetM();
float m = std::clamp(m_slope_ * (child_m - parent_m_), -m_cap_, m_cap_);
m *= FastSign(-q);
m *= a_constant_ + a_linear_ * std::abs(q) + a_square_ * q * q;
return m;
if (child.GetN() == 0) return GetDefaultMUtility();
return GetMUtility(child.node(), q);
}

// The M utility to use for unvisited nodes.
float GetDefaultM() const { return 0.0f; }
float GetDefaultMUtility() const { return 0.0f; }

private:
static bool WithinThreshold(const Node* parent, float q_threshold) {
Expand Down Expand Up @@ -436,10 +439,13 @@ std::vector<std::string> Search::GetVerboseStats(Node* node) const {
up = -up;
std::swap(lo, up);
}
*oss << (lo == up ? "(T) "
: lo == GameResult::DRAW && up == GameResult::WHITE_WON ? "(W) "
: lo == GameResult::BLACK_WON && up == GameResult::DRAW ? "(L) "
: "");
*oss << (lo == up
? "(T) "
: lo == GameResult::DRAW && up == GameResult::WHITE_WON
? "(W) "
: lo == GameResult::BLACK_WON && up == GameResult::DRAW
? "(L) "
: "");
}
};

Expand All @@ -449,7 +455,7 @@ std::vector<std::string> Search::GetVerboseStats(Node* node) const {
: MEvaluator();
for (const auto& edge : edges) {
float Q = edge.GetQ(fpu, draw_score);
float M = m_evaluator.GetM(edge, Q);
float M = m_evaluator.GetMUtility(edge, Q);
std::ostringstream oss;
oss << std::left;
// TODO: should this be displaying transformed index?
Expand Down Expand Up @@ -862,7 +868,7 @@ void Search::PopulateCommonIterationStats(IterationStats* stats) {
for (const auto& edge : root_node_->Edges()) {
const auto n = edge.GetN();
const auto q = edge.GetQ(fpu, draw_score);
const auto m = m_evaluator.GetM(edge, q);
const auto m = m_evaluator.GetMUtility(edge, q);
const auto q_plus_m = q + m;
stats->edge_n.push_back(n);
if (n > 0 && edge.IsTerminal() && edge.GetWL(0.0f) > 0.0f) {
Expand Down Expand Up @@ -1599,13 +1605,13 @@ void SearchWorker::PickNodesToExtendTask(
int index = child->Index();
visited_pol += current_pol[index];
float q = child->GetQ(draw_score);
current_util[index] = q + m_evaluator.GetM(child, q);
current_util[index] = q + m_evaluator.GetMUtility(child, q);
}
const float fpu =
GetFpu(params_, node, is_root_node, draw_score, visited_pol);
for (int i = 0; i < max_needed; i++) {
if (current_util[i] == std::numeric_limits<float>::lowest()) {
current_util[i] = fpu + m_evaluator.GetDefaultM();
current_util[i] = fpu + m_evaluator.GetDefaultMUtility();
}
}

Expand Down