A group's orbit-integrator repository records the following history
PHYSICS · Multi-part · Fermi University Physics · Computational Physics · Research software practice, verification and validation · Research software practice, verification and validation
Scientific Computing for Physicists, Ch A repository others can build on: collaboration, history and workflows
Problem
A group's orbit-integrator repository records the following history. On main, commit C1 adds a Verlet step. Branch energy-test is created from C1 and gains two commits: C2, which changes the half-step velocity update, then C3, which adds an energy-conservation test. Meanwhile one commit C4 is made directly on main, independent of the branch's changes. Finally energy-test is merged back into main, producing a new commit C5. Draw the resulting commit graph.
((a)) List the parent commit(s) of C5.
((b)) State whether the merge is a fast-forward or a true merge, and justify this from the graph.