  This letter reports some new identities for multisoliton potentials that are
based on the explicit representation provided by the Darboux matrix. These
identities can be used to compute the complex gradient of the energy content of
the tail of the profile with respect to the discrete eigenvalues and the
norming constants. The associated derivatives are well defined in the framework
of the so-called Wirtinger calculus which can aid a complex variable based
optimization procedure in order to generate multisolitonic signals with desired
effective temporal and spectral width.
