Abstract:
By including spectral functions, we obtain nonlocal symmetries equivalent to Lie point symmetries of the corresponding extended systems for the Boussinesq equation, the modified generalized Vakhnenko equation, the Hirota–Satsuma equation, and the Sawada–Kotera equation. All considered equations have third-order Lax pairs, which allows studying their nonlocal symmetries in a unified way.
This research was supported by the Natural Science
Foundation of Zhejiang Province (No. LQ20A010009), General Scientific
Research of Zhejiang Province (No. 201909003329), National Natural Science
Foundation of China (No. 11675055), and Natural Science Foundation of
Shanghai (No. 19ZR1414000).