if(myBC == 1)
    Tleft = 393; Tright = 293; 

T(1,:) = T(2,:); T(Ny,:) = T(Ny-1,:); 
T(iny,1)= 2*Tleft - T(iny,2); T(iny,Nx)=2*Tright - T(iny,Nx-1);

elseif(myBC == 4)
    Tleft = 293; Ttop = 330; Tbot = 330;
    
T(1,:) = 2*Ttop - T(2,:); % now 0.5*(T(1,:)+T(2,:))=Ttop -> Ts=fixed
T(Ny,:) = 2*Tbot - T(Ny-1,:); 
T(iny,1)= 2*Tleft - T(iny,2); 
T(iny,Nx)= T(iny,Nx-1);   % at outlet dTdx = 0 - a usual outlet bc
   
end