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John Edensor Littlewood was a mathematician whose work with Godfrey Harold Hardy connected analysis, inequalities, series and the Riemann zeta function. Their collaboration helped develop the Hardy-Littlewood circle method for arithmetic counting problems. He also worked with Mary Cartwright on nonlinear ordinary differential equations motivated by radio engineering, including the Van der Pol equation.^[ref] Their investigations of strongly driven oscillators helped reveal how a deterministic dynamical system can have complicated long-term behavior. This makes his work a bridge between the estimates of classical analysis and the geometric study of dynamical systems.

Mary Cartwright studied analysis and nonlinear ordinary differential equations. With John Edensor Littlewood, she investigated forced oscillators of the Van der Pol equation type, where state-dependent damping and external periodic forcing interact.^[ref]

The motivation included radio engineering: a nonlinear oscillator need not respond like a linear resonator. Studying its long-term solutions requires understanding the dynamics over repeated forcing cycles, not just solving one instantaneous balance. Cartwright's own historical account describes this exchange between an engineering question and qualitative mathematics.^[ref]