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
Velocity (software development) more like the concept of directionless “speed” from physics. A third problem with velocity is that it is often misused as a measure of efficiency or team performance. Velocity is a metric of work done, not efficiency. Velocity can be increased by working overtime or adding team members, neither of which necessarily increase efficiency or performance. In summary, velocity is a problematic metric because it is easy to manipulate and often misused as an indicator of efficiency. Velocity (software development) Velocity is a metric for work done, which is often used in agile software development. Measuring velocity is sometimes called