add exercise

slides/pages/recap.md

@@ -264,3 +264,19 @@ In general, error checking in simple programs is redundant.
 ### Demo
 
 See live demo in the tutorial.
+
+---
+title: MPI VIII
+layout: center
+---
+
+## Exercise
+
+Pass around the token value by all processes in a ring-like fashion.
+
+E.g. for 4 processes:
+
+token -> 0 -> 1 -> 2 -> 3 -> 0 -> token
+
+Add all missing function calls in `exercises/MPI_examples/round_trip/round_trip.c`
+