calculus of variations
A field of mathematical analysis dealing with maximizing or minimizing functionals, typically involving integrals.
変分学は最適制御理論の基礎となる分野だ。
The calculus of variations is a field that forms the basis of optimal control theory.
Compound of 変分 (henbun, 'variation') + 学 (gaku, 'study'). The term is a direct translation of the English 'calculus of variations'.