> The cost is measured in an exact complex-register model that assigns unit cost to exact complex field operations. The algorithm accepts every x ∈ Cn, with no bound on its entries or on intermediate complex magnitudes. Its computation on the input uses only addition, subtraction, and multiplication by prepared input-independent scalars. The magnitudes of those scalar coefficients are unrestricted as well.
I'm not very familiar with this kind of low-level theoretical computer science, so please forgive my possibly stupid question: is it common to use a model of computation like this, with registers which can store exact complex numbers? Since no computers like that really exist, would that limit the practical application of this finding?