This function generates rectangular mesh accoarding to grid set by vectors xx and yy.

function [Nodes, Rectangles]=Rectangles_Mesh(xx,yy)
where inputs
xx and yy are vectors for grids of size (Nx,1) and (Ny,1), respectively.
output:
Nodes (Nx*Ny,2) is a matrix of x-coordinate of y-coordinates of the mesh nodes.
Rectangles((Nx-1)*(Ny-1),4) is a matrix of nodes connectivity for each element in counter clockwise direction.