The above relation shows that the determination of the entropy requires knowledge of the heat capacity and the equation of state (which is the relation between "P","V", and "T" of the substance involved). Normally these are complicated functions and numerical integration is needed. In simple cases it is possible to get analytical expressions for the entropy. In the case of an ideal gas, the heat capacity is constant and the ideal gas law gives that , with the number of moles and "R" the molar ideal-gas constant. So, the molar entropy of an ideal gas is given by