spatial grid points division

I have (N = 550) grid points starts from a = 0, to the end point b = 291.5. the spatial grid step is dx = 0.53. I want increase the grids between a and b by decreasing dx, without changing N.

Here the codes i used

N   = 550;      % number of grid points
x   = linspace(a, b, N+1)';      % cell interfaces
dx  = x(2) - x(1);                  % spatial grid step
xc  = 0.5*(x(1:end-1) + x(2:end));  % centers of cells

[Guillaume]

I don't understand what you want. If you decrease the grid spacing dx, the numbers of points N must go up or your end points must get closer. It's not possible to decrease dx without changing a, b, or N.

[Ahmed Abdalazeez]

But I can't change N, because the stability of the solution, otherwise the system will be unstable.

[Guillaume]

By definition

dx = (b-a) / N

So again, you can't change dx without changing at least one variable on the other side of the equation.