Why is rpy error integral computed in that particular order

[praneelacharya]

While going through the DSLPIDControl.py base class. I noticed integral of roll pitch yaw error to be computed as previous roll pitch yaw error - rot_e * dt. Where, rot_e are the diagonal elements of the rotation matrix error. Why not do something like self.integral_rpy_e = self.integral_rpy_e + rpy_rates_e*control_timestep. As a learner I am just curious as what could be the motivation.

_dslPIDAttitudeControl(self,
control_timestep,
thrust,
cur_quat,
target_euler,
target_rpy_rates
):
"""DSL's CF2.x PID attitude control.

........
self.integral_rpy_e = self.integral_rpy_e - rot_e*control_timestep