% Solving the Poisson's equation on a unit square 0<x<1, 0<y<1 with the 
% Dirichlet boundary conditions using the uniform grid discretisation and
% various iteration schemes.
% You have to complete the lines with comments in CAPITAL letters.
%***********************************************************************
close all        %closes all windows opened during the previous runs
clear all        % clears the memory from the results of previous runs
clc              % clears the screen
nx=              %the number of discretisation points in x direction 
ny=nx            %the number of discretisation points in y direction 
h=1/(nx-1)       %the discretisation step size
x=               %X-GRID
y=               %Y-GRID
Un=              %INITIAL GUESS
Un(1:nx,1)=      %LOWER BC
Un(1:nx,ny)=     %UPPER BC
Un(1,1:ny)=      %LEFT BC
Un(nx,1:ny)=     %RIGHT BC
tol=             %TERMINATION CRITERION (ACCURACY REQUIRED)
for j=2:ny-1
   for i=2:nx-1
      r(i,j)=    %RIGHT-HAND SIDES
   end
end
Unold=Un;        %results of the previous iteration are stored here
Unold(2,2)=10;   %EXPLAIN WHY THIS LINE IS NECESSARY
it=0;            %initialising the iteration counter
%c=               %OPTIMAL PARAMETERS FOR SOR 
%om=              % ITERATIONS
while            %ITERATION LOOP and STOPPING CRITERION
   it=it+1;      %iteration counter
   Unold=Un;     %updating the previous iteration values
   for j=2:ny-1
      for i=2:nx-1
%you should have uncommented only lines for the one iteration type at a time
%%JACOBI ITERATIONS
         Un(i,j)=
%%GAUSS-SEIDEL ITERATIONS
%         Un(i,j)=
%SOR ITERATIONS
%         Un(i,j)=
      end
   end
end
it    %prints out the total number of iterations
Un'   %prints out the solution array (transposed to relate it easier to the
      %computational domain geometry)