Added DiscreteValues file

gtsam/discrete/DiscreteValues.h

@@ -0,0 +1,37 @@
+/* ----------------------------------------------------------------------------
+
+ * GTSAM Copyright 2010, Georgia Tech Research Corporation,
+ * Atlanta, Georgia 30332-0415
+ * All Rights Reserved
+ * Authors: Frank Dellaert, et al. (see THANKS for the full author list)
+
+ * See LICENSE for the license information
+
+ * -------------------------------------------------------------------------- */
+
+/**
+ *  @file DiscreteValues.h
+ *  @date Dec 13, 2021
+ *  @author Frank Dellaert
+ */
+
+#pragma once
+
+#include <gtsam/discrete/Assignment.h>
+#include <gtsam/inference/Key.h>
+
+namespace gtsam {
+
+/** A map from keys to values
+ * TODO(dellaert): Do we need this? Should we just use gtsam::DiscreteValues?
+ * We just need another special DiscreteValue to represent labels,
+ * However, all other Lie's operators are undefined in this class.
+ * The good thing is we can have a Hybrid graph of discrete/continuous variables
+ * together..
+ * Another good thing is we don't need to have the special DiscreteKey which
+ * stores cardinality of a Discrete variable. It should be handled naturally in
+ * the new class DiscreteValue, as the variable's type (domain)
+ */
+using DiscreteValues = Assignment<Key>;
+
+}  // namespace gtsam