function [u_new,v_new,h_new] = forward_backward(u,v,h,g,f,H,dt,dx)
%forward_backward computes a single forward time step forin the rotating
% SW system
%   h is assumed staggered dx/2 to the left of u and v
u_new = u + dt*( f*v-g*(circshift(h,-1)-circshift(h,0))/dx ); 
v_new = v - dt*f*u_new;
h_new = h - dt*( H*(circshift(u_new,0)-circshift(u_new,1))/dx );



