Creation of conductance matrix between boundary elements and CG of the tetrahedron

The conductance matrix between boundary elements of the tetrahedron has 6 conductances, while the matrix between CG and boundary elements has ten conductances. When a tetrahedron has a linear temperature gradient, the temperature at its CG is equal to the average temperature of the midpoints of the side surfaces, which gives the following equations to compute the additional conductances between the CG and boundary elements:

where GiCG is the conductance between the boundary elements and CG.

The root mean square value of the sum of the conductances between boundary elements and the CG is minimized by:

where G12, G13, G14, G23, G24, and G34 are the conductances between boundary elements in the transformed matrix.

The star-delta transformation is used to connect the conductances between boundary elements to the conductances between CG and boundary elements as: