imu initialization question

[lturing]

firstly, thanks for this great work!
recently, i read imu initialized codes, i find some questions
likes here, take an example

A.block<3, 3>(i * 6, 0) =  -0.5 * delta.t * delta.t * matrix<3>::Identity();

i think it should be

A.block<3, 3>(i * 6, 0) += -0.5 * delta.t * delta.t * matrix<3>::Identity();

do i miss some parts?