The entropy of a thermodynamic graph

We introduce an algorithmic model of heat conduction, the thermodynamic graph. The thermodynamic graph is analogous to meshes in the finite difference method in the sense that the calculation of temperature is carried out at the vertices of the graph, and the edges indicate the direct heat exchange between the vertices. Recurrence relations of heat conduction in graph are derived without using of differential equations and based on the coefficients of thermal conductivity and heat capacity. This approach seems to be more direct and flexible from the point of view of algorithmic modeling of thermodynamic process than the derivation of difference schemes from differential equations. We introduce also the notion of entropy of thermodynamic graph. We find the maximum length of the time step at which the entropy does not decrease in the general case. As a result, this give us the accurate boundary of the model stability.