Dear all,

I have a question on the step-35
<https://dealii.org/current/doxygen/deal.II/step_35.html> when I learn it.
the step use project method to solve NS equation. And for updating the
pressure step, there is a Rotational Form
<https://dealii.org/current/doxygen/deal.II/step_35.html#:~:text=Incremental%20Method%20in%20Rotational%20Form.%20In%20this%20case>.
In the function of update_pressure(const bool reinit_prec), it seem it plus
the rotational term(+1/Re*div u), while the formula is minus(-1/Re*div u),
the pres_tmp is calculated at projection_step
<https://dealii.org/current/doxygen/deal.II/step_35.html#:~:text=%C2%A0%20%20%20%20%20for%20(unsigned%20d%20%3D%200%3B%20d%20%3C%20dim%3B%20%2B%2Bd)-,pres_Diff%5Bd%5D.Tvmult_add(pres_tmp%2C%20u_n%5Bd%5D)%3B,-phi_n_minus_1%20%3D%20phi_n%3B>,
and is pres_tmp is (div u).

I want to know why here is plus not minus. Maybe the minus sign was
included in the original code I didn't notice or understand.

Could anyone help me out?

Best,
Chen

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