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 (10[1])of the fact that the expectation of a Hermitian matrix is bounded below by its lowest eigenvalue. (10[1])An approximation method named for this word minimizes the energy of a trial wavefunction with respect (10[1])to a parameter. (10[2])The Beltrami (10[1])identity is key to a subfield of mathematical analysis whose name includes this plural noun, (10[1])which uses the Euler–Lagrange equation (10[1])to find the extrema of functionals (-5[1])like the action (10[1])in Lagrangian mechanics. The brachistochrone problem (10[1])motivated the development of, for 10 points, the “calculus of” what word, (10[1])meaning small changes (10[1]-5[1])to functions? (10[1]0[9])■END■