Bright soliton of the focusing nonlinear Schrödinger equation (source code)

= Bright soliton of the focusing nonlinear Schrödinger equation

For negative frequency $E$, the one-dimensional focusing nonlinear Schrödinger equation has the localized stationary profile
$$
f_E(x)=\sqrt{2|E|}\operatorname{sech}(\sqrt{2|E|}x).
$$
Galilean boosts generate moving profiles with a translational collective coordinate and constant velocity.