When total energy and the endpoints are fixed, Maupertuis's least action principle applies. For example, to score points in basketball the ball must leave the shooters hand and go through the hoop, but the time of the flight is not constrained. Maupertuis's least action principle is written mathematically as the stationary condition ( δ δ W ) E = 0 on the abbreviated action W [ q ] = def ∫ ∫ q 1 q 2 p ⋅ ⋅ d q , (sometimes written S 0 ), where p = ( p 1 , p 2 , … … , p N ) are the particle momenta or the conjugate momenta of generalized coordinates, defined by the equation p k = def ∂ ∂ L ∂ ∂ q ˙ ˙ k , where L ( q , q ˙ ˙ , t ) is the Lagrangian. Some textbooks write ( δ δ W ) E = 0 as Δ Δ S 0 , to emphasize that the variation used in this form of the action principle differs from Hamilton's variation. Here the total energy E is fixed during the variation, but not the time, the reverse of the constraints on Hamilton's principle. Consequently, the same path and end points take different times and energies in the two forms. The solutions in the case of this form of Maupertuis's principle are orbits : functions relating coordinates to each other in which time is simply an index or a parameter.