Add predicate concept

Classification/doc/Classification/Concepts/Predicate.h

@@ -0,0 +1,34 @@
+namespace CGAL
+{
+
+namespace Classification
+{
+
+/*!
+\ingroup PkgClassificationConcepts
+\cgalConcept
+
+Concept describing a predicate used by classification functions (see
+`CGAL::classify()`, `CGAL::classify_with_local_smoothing()` and
+`CGAL::classify_with_graphcut()`).
+
+\cgalHasModel `CGAL::Classification::Sum_of_weighted_features_predicate`
+\cgalHasModel `CGAL::Classification::Random_forest_predicate`
+
+*/
+class Predicate
+{
+public:
+
+  /*!
+    \brief Returns, for each label indexed from 0 to `out.size()`, the
+    probability of the point at `item_index` to belong to this label.
+   */
+  void probabilities (std::size_t item_index, std::vector<double>& out) const;
+
+
+};
+
+} // namespace Classification
+
+} // namespace CGAL