Replace nested loops with a matrix

I have to optimize this code but i am not sure how to turn it into a matrix.

for i=2:nhx-1
    for j=2:nhy-1
        U(i,j)= U(i,j)-dt*(Pc(i+1,j)-Pc(i-1,j))/(2*hx);
    end
end

Answer 1

[Bruno Luong]

i=2:nhx-1;
j=2:nhy-1;
U(i,j)= U(i,j)-dt*(Pc(i+1,j)-Pc(i-1,j))/(2*hx);

[Mohammad Ezzad Hamdan]

Thank you!

Answer 2

[Dyuman Joshi]

Unew = zeros(nhx, nhy);
Unew(2:nhx-1, 2:nhy-1)=U(2:nhx-1, 2:nhy-1)-dt.*(P(3:nhx,2:nhy-1)-P(1:nhx-2,2:nhy-1))./(2*hx);

Source

[Mohammad Ezzad Hamdan]

Thank you!