Fix one more bug with root node with all weightless children causing …

…genmove to fail

cpp/configs/gtp_human9d_search_example.cfg

@@ -44,6 +44,8 @@ resignMinMovesPerBoardArea = 0.40
 # This is due to the strong bias of the human SL network.
 # You can reduce this number if you are on weaker hardware. It may reduce strength a bit but will still
 # provide a huge strength boost over using the humanSL network alone as in gtp_human5k_example.cfg
+# It's NOT recommended to reduce this below about 30-40 visits, since that will result in too few explorations of a variety of moves.
+# If you want to adjust strength, see humanSLChosenMovePiklLambda instead.
 maxVisits = 400   # 40 in gtp_human5k_example.cfg.
 
 # Having more than one thread speeds up search when visits are larger.
@@ -67,7 +69,7 @@ humanSLChosenMoveIgnorePass = true
 # this may still produce a very strong player.
 # To calibrate for some but less strength gain, it will take experimentation - in addition to increasing this value a lot,
 # you can also try using old/small KataGo nets (e.g. b6c96, b10c128), reducing visits (though reducing below about 30-40
-# is not recommended), or using the humanSLModel itself as the main "-model".
+# is NOT recommended), or using the humanSLModel itself as the main "-model".
 humanSLChosenMovePiklLambda = 0.06  # was 100000000 in gtp_human5k_example.cfg.
 
 # Spend 80% of visits to explore humanSL moves to ensure they get evaluations to use with humanSLChosenMovePiklLambda

cpp/search/searchresults.cpp

@@ -295,8 +295,21 @@ bool Search::getPlaySelectionValues(
       maxValue = playSelectionValues[i];
   }
 
-  if(maxValue <= 1e-50)
-    return false;
+  if(maxValue <= 1e-50) {
+    //If we reached this point we have nonzero many children but the children are all weightless.
+    //In that case, at least set each one to be weighted by its policy.
+    for(int i = 0; i<numChildren; i++) {
+      playSelectionValues[i] = std::max(0.0,(double)policyProbs[getPos(locs[i])]);
+    }
+    //Recompute max
+    for(int i = 0; i<numChildren; i++) {
+      if(playSelectionValues[i] > maxValue)
+        maxValue = playSelectionValues[i];
+    }
+    if(maxValue <= 1e-50) {
+      return false;
+    }
+  }
 
   //Sanity check - if somehow we had more than this, something must have overflowed or gone wrong
   assert(maxValue < 1e40);