fix: normalize probabilities for entropy

Author: ooples

src/Models/Results/PredictionModelResult.cs

@@ -1243,13 +1243,42 @@ private static Vector<T> ComputePerSampleEntropy(Vector<T> probabilitiesFlat, in
         var numOps = MathHelper.GetNumericOperations<T>();
         var entropy = new Vector<T>(batch);
         var eps = numOps.FromDouble(1e-12);
+        var sumTolerance = numOps.FromDouble(1e-6);
 
         for (int b = 0; b < batch; b++)
         {
+            var sumP = numOps.Zero;
+            for (int c = 0; c < classes; c++)
+            {
+                var p = probabilitiesFlat[b * classes + c];
+                if (numOps.LessThan(p, numOps.Zero))
+                {
+                    p = numOps.Zero;
+                }
+                sumP = numOps.Add(sumP, p);
+            }
+
+            if (numOps.LessThan(sumP, eps))
+            {
+                entropy[b] = numOps.Zero;
+                continue;
+            }
+
+            var shouldNormalize = numOps.GreaterThan(numOps.Abs(numOps.Subtract(sumP, numOps.One)), sumTolerance);
+            var denom = shouldNormalize ? sumP : numOps.One;
+
             var h = numOps.Zero;
             for (int c = 0; c < classes; c++)
             {
                 var p = probabilitiesFlat[b * classes + c];
+                if (numOps.LessThan(p, numOps.Zero))
+                {
+                    p = numOps.Zero;
+                }
+                if (shouldNormalize)
+                {
+                    p = numOps.Divide(p, denom);
+                }
                 if (numOps.LessThan(p, eps))
                 {
                     p = eps;