Article

**Discrete Contin. Dyn. Syst. 26:1, 151-196 (2010)**[DOI: 10.3934/dcds.2009.26.151]

## The algebro-geometric initial value problem for the Ablowitz-Ladik hierarchy

### Fritz Gesztesy, Helge Holden, Johanna Michor, and Gerald Teschl

We discuss the algebro-geometric initial value problem for the Ablowitz-Ladik hierarchy
with complex-valued initial data and prove unique solvability globally in
time for a set of initial (Dirichlet divisor) data of full measure. To this effect we develop a new algorithm for constructing stationary complex-valued algebro-geometric solutions of the Ablowitz-Ladik hierarchy, which is of independent interest as it solves the inverse
algebro-geometric spectral problem for general (non-unitary) Ablowitz-Ladik Lax operators, starting from a suitably chosen set of initial divisors of full measure. Combined with an appropriate first-order system of differential equations with respect to time (a substitute for the well-known Dubrovin-type equations), this yields the construction of global algebro-geometric solutions of the time-dependent Ablowitz-Ladik hierarchy.

The treatment of general (non-unitary) Lax operators associated with general coefficients for the Ablowitz-Ladik hierarchy poses a variety of difficulties that, to the best of our knowledge, are successfully overcome here for the first time. Our approach is not confined to the Ablowitz-Ladik hierarchy but applies generally to *(1+1)*-dimensional completely integrable soliton equations of differential-difference type.

** MSC2000:** Primary 37K10, 37K20, 47B36; Secondary 35Q58, 37K60.

**Keywords:** *Ablowitz-Ladik hierarchy, complex-valued solutions, initial value problem.*

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