This is the first word in the name of a hybrid quantum-classical algorithm introduced by Peruzzo et al. with the most promising near-term potential for speeding up computational chemistry calculations. That “quantum eigensolver” described by this word takes advantage of the fact that the expectation of a Hermitian matrix is bounded below by its lowest eigenvalue. An approximation method named for this word minimizes the energy of a trial wavefunction with respect to a parameter. (10[1])The Beltrami identity is key to a subfield of mathematical analysis whose name includes this plural noun, which uses the Euler–Lagrange equation to find the extrema of functionals like the action in Lagrangian mechanics. The brachistochrone problem motivated the development of, for 10 points, the “calculus of” what word, meaning small changes (-5[1])to functions? (0[1])■END■