Nonlinear wave equations and constrained harmonic motion.
The study of the Korteweg-deVries, nonlinear Schrödinger, Sine-Gordon, and Toda lattice equations is simply the study of constrained oscillators. This is likely to be true for any nonlinear wave equation associated with a second-order linear problem.
Deift
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Courant Institute of Mathematical Sciences, New York University, New York 10012.
Lund
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Trubowitz
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