change sign

Author: Yuheng Tu

src/helm/benchmark/reeval_runner.py

@@ -82,7 +82,7 @@ def _estimate_model_ability(
     ) -> float:
         def closure():
             optim.zero_grad()
-            probs = torch.sigmoid(ability - difficulties)
+            probs = torch.sigmoid(ability + difficulties)
             loss = -torch.distributions.Bernoulli(probs=probs).log_prob(responses).mean()
             loss.backward()
             return loss