Now, substituing into (27.5) using (29.3) and (29.4) produces
where, Eq. (29.5) is basically a discrete form of Poisson equation that is equivalent to
It may be noted that the solution converges as Eq. (29.3) and (29.4) can be also represented as
The algorithm may be summarized as
into (27.5) using (29.3) and (29.4) produces 
Eq. (29.5) is basically a discrete form of Poisson equation that is equivalent to 
Eq. (29.3) and (29.4) can be also represented as 
is obtained from equation (29.5) 
is obtained from 
where 
is a relaxation parameter. 
