%-----------------------------------------------------------------------
% Example 9.7.3: Electrostatic Field 
%-----------------------------------------------------------------------

% Initialize 

   clc                  % clear scree
   clear                % clear variables
   global a b
   a = 1;               % width (m) 
   b = 1;               % length (m)  
   m = 30;              % number of x grid points 
   n = 30;              % number or y grid points 
   q = 100;             % maximum number of iterations 	
   tol = 1.0e-5;        % error tolerance 
   x = zeros (m,1);     % x axis grid points (m) 
   y = zeros (n,1);     % y axis grid points (m) 	
   U = zeros (m,n);     % electrostatic potential (V) 

% Solve Poisson equation 

   fprintf ('Example 9.7.3: Electrostatic Field\n'); 
   plotfun (0,a,0,b,'Charge Density','x','y','f(x,y)','funf973')
   [alpha,r,x,y,U] = poisson (a,b,m,n,q,tol,'funf973','');
   show ('Relaxation parameter alpha',alpha)
   show ('Number of iterations',r)
   plotxyz (x,y,U,'Electrostatic Field','x (cm)','y (cm)','u (V)')

%-----------------------------------------------------------------------