Crank-Nicolson scheme for Navier-Stokes Equation

Hi, all, I’m learning the code from this site

The code use Crank-Nicolson scheme to do temporal discretization for NSE and then solve it.

My question is that why the two lines (marked use red line) are the same? Is it correct or the grad(u) in the second line should be grad(u_old)?

Thanks for your help.

That seems like a typo to me.

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