How to loop half matrix

for i=2:nhx-1
    for j=2:nhy-1
        
      Unew(i,j) = U(i,j)-dt*(P(i+1,j)-P(i-1,j))/(2*hx)...
        +nu*dt*(1/(hx*hx)*(U(i+1,j)-2.*U(i,j)+U(i-1,j))...
               +1/(hy*hy)*(U(i,j+1)-2.*U(i,j)+U(i,j-1)))...
	-dt*U(i,j)/(hx)*(U(i,j)-U(i-1,j))...
        -dt*V(i,j)/(2*hy)*(U(i,j+1)-U(i,j-1));
    
    end
end

Hi, the Unew produce something like this "1 2 3 4 5 4 3 2 1" as an example. I would like to calculate just half of the j domain so that Unew will produce "1 2 3 4 5" and the following ''4 3 2 1" will just be reflected from "1 2 3 4" in order to shorten the running time.

Answer 1

[Jan]

for i = 2:nhx-1
    for j = 2:(nhy + 1) / 2
        Unew(i, j) = ...
        Unew(i, nhy - j + 1) = Unew(i, j);
    end
end

[Mohammad Ezzad Hamdan]

Thanks Jan!!!