I'm here for help and hope somebody could give a hand on this because I'm noob in this.

I'm now constructing a MATLAB program to find Electrical field and potential within a square grid mesh with square cavity inside.

like the picture above.

I only manage up to this

v2=100.0;

%set no. of iteration

ni=1;

%nx=no. of x grid points

nx=8;

%ny=no. of y grid points

ny=6;

%set mesh size

d=5;

%nm=no of x grid for cavity

nm=4;

%nn=no of y grid for cavity

nn=3;

%set initial values equal to zeroes

v=zeros(nx+2,ny+2);

u=(nx-(nm-1));

t=(ny-(nm-1));

%fix potential at fixed nodes

for i=u:nx+1

v(i,t-1)=v2;

end

for j=t:ny+1

v(u-1,j)=v2;

end

head=['Iteration Coordinate Potential East North West South Electric field '

' Ex Ey'];

disp(head)

for k=1:ni

for u=2:nx+1

for t=2:ny+1

v(u,t)=0.25*(v(u,t)+v(u-1,t)+v(u,t+1)+v(u,t-1)+2*d^2);

Ex=(v(u+1,t)-v(u-1,t))/(2*d);

Ey=(v(i,u+1)-v(u,t-1))/(2*d);

fprintf('\t%5g \t(%g,%g) \t%5g \t%5g \t%5g \t%5g \t%5g \t%5g \t%5g \n ',k,u,t,v(u,t),v(u+1,t),v(u,t+1),v(u-1,t),v(u,t-1),Ex,Ey);

end

end

end

It seems that I'm now stuck where should i put a restriction to where the cavity is(that means, the program should not be calculating the V at that nodes)

can you give me some ideas how should i proceed with this?

thanks in advance.

regards