Clarified which code needs modification for phase 5

project/phase5.md

@@ -3,7 +3,7 @@
 
 # Phase 5: Group Optimization
 
-For this assignment, you will discuss what you did to speed up the C++ program from the [first optimization assignment](phase3.md) in groups of 3-5, and **spend a at least 3 more hours using your group's insights to optimize the program a bit more**.
+For this assignment, you will discuss what you did to speed up the C++ program from the [first optimization assignment](phase3.md) in groups of 3-5, and **spend a at least 3 more hours using your group's insights to optimize the program a bit more**. You only need to modify `optimize.cpp` (or whichever code results in your `optimize` binary), not `wavesolve*`.
 
 The "discussion" can take any reasonable form you would like, ranging from sharing your notes and a few messages on Slack to meeting in person for three hours to work on optimizing your programs together. By default I will assign your groups randomly, but if you have partners in mind send me a message to let me know your choice of group.