I've googled some knowledge about FDM method for solving Laplace equations (since I have to solve this problem numerically using SciLab) and for rectangular rod I've obtained the following equation (in Cartesian coordinates):
T_{i+1,j} + T_{i-1,j} + T_{i,j+1} + T_{i,j-1} + 4T_{i,j} = 0...