Effective mass (solid-state physics) from both sides gives where is the th element of , is the th element of , and are the th and th elements of , respectively, and is the total energy of the particle according to the Planck–Einstein relation. The index is contracted by the use of Einstein notation (there is an implicit summation over ). Since Newton's second law uses the inertial mass (not the gravitational mass), we can identify the inverse of this mass in the equation above as the tensor This tensor expresses the change in group velocity due to a change in crystal momentum. Its
Binary mass function the true orbital velocity is low (implying low mass objects) and the inclination high (the orbit is seen edge-on), or that the true velocity is high (implying high mass objects) but the inclination low (the orbit is seen face-on). The peak radial velocity formula_1 is the semi-amplitude of the radial velocity curve, as shown in the figure. The orbital period formula_2 is found from the periodicity in the radial velocity curve. These are the two observable quantities needed to calculate the binary mass function. The observed object of which the radial velocity can be measured is taken to be object