Abstract
We address the problem of equipartition in a long Fermi–Pasta–Ulam (FPU) chain. After giving a precise relation between FPU and Korteweg–de Vries we use the latter equation to show that, corresponding to initial data à la Fermi, the time average of the energy on the kth mode decreases exponentially with k∕N. The result persists in the thermodynamic limit.