+/** \ingroup TRACE_user_variables
+ * \brief Declare a new user variable associated to links.
+ *
+ * Declare a user variable that will be associated to links.
+ * A user link variable can be used, for example, to trace
+ * user variables such as the number of messages being
+ * transferred through network links. The color
+ * associated to this new variable will be random.
+ *
+ * \param variable The name of the new variable to be declared.
+ *
+ * \see TRACE_link_variable_declare_with_color
+ */
+void TRACE_link_variable_declare (const char *variable)
+{
+ instr_user_variable (0, NULL, variable, "LINK", 0, INSTR_US_DECLARE, NULL, user_link_variables);
+}
+
+/** \ingroup TRACE_user_variables
+ * \brief Declare a new user variable associated to links with a color.
+ *
+ * Same as #TRACE_link_variable_declare, but associated a color
+ * to the newly created user link variable. The color needs to be
+ * a string with three numbers separated by spaces in the range [0,1].
+ * A light-gray color can be specified using "0.7 0.7 0.7" as color.
+ *
+ * \param variable The name of the new variable to be declared.
+ * \param color The color for the new variable.
+ *
+ */
+void TRACE_link_variable_declare_with_color (const char *variable, const char *color)