Update app.py

app.py

@@ -157,10 +157,15 @@ add_password_gate()
 def rmse(y_true, y_pred) -> float:
     return float(np.sqrt(mean_squared_error(y_true, y_pred)))
 
-def pearson_r(y_true, y_pred) -> float:
+    def pearson_r(y_true, y_pred) -> float:
     a = np.asarray(y_true, dtype=float)
     p = np.asarray(y_pred, dtype=float)
-    if a.size < 2: return float("nan")
+    
+    # Check for constant arrays, where std dev would be zero.
+    # We must check both true and predicted arrays.
+    if a.size < 2 or np.all(a == a[0]) or np.all(p == p[0]):
+    return float("nan")
+        
     return float(np.corrcoef(a, p)[0, 1])
 
 @st.cache_resource(show_spinner=False)