Add simulation type context to RK4 comment

src/physics.h

@@ -38,6 +38,10 @@ Mat3 mat3_rotation_orbital(double omega, double i, double Omega);
 Vec3 calculate_acceleration(Vec3 force, double mass);
 
 // Physics integration functions
+// RK4 inferior to analytical propagation for orbit simulation
+// In our specific simulation (2-body with SOI patched conics):
+// Analytical: <1e-12 energy drift vs RK4: 2e-7 to 5e-3
+// See tests/test_hybrid_energy_conservation.cpp for comparison
 void rk4_step(Vec3* position, Vec3* velocity, double dt,
               double body_mass, double parent_mass);
 Vec3 evaluate_acceleration(Vec3 relative_pos, double body_mass, double parent_mass);