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Gruber P. Convex and Discrete Geometry

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27 Special Problems in the <strong>Geometry</strong> of Numbers 409<br />

This function was first studied by Epstein [305] <strong>and</strong> re-discovered by Sobolev [945].<br />

It is important for the determination of potentials of crystal lattices, for the lattice<br />

energy, for the dynamics of viscous fluids, <strong>and</strong> for the numerical integration<br />

of functions belonging to Sobolev classes. Its study, in the context of the geometry<br />

of numbers, was cultivated in the 1950s <strong>and</strong> 1960s <strong>and</strong> later in Great Britain <strong>and</strong> in<br />

Russia. The motive for the study in Great Britain was purely number-theoretic, while<br />

the Russian school of the geometry of numbers studied it following a suggestion of<br />

Sobolev in the context of the problem of the optimal choice of nodes for numerical<br />

integration formulae.<br />

In the following we describe some of the developments induced by Mordell’s<br />

problem. For more information <strong>and</strong> references the reader is referred to [447] <strong>and</strong><br />

Narzullaev <strong>and</strong> Ramharter [765]. In addition, we state some results on local minima<br />

of the Epstein zeta-function. See also [447] <strong>and</strong> the report [438].<br />

Mordell’s Inverse Problem<br />

Given a lattice L in E d ,let<br />

Using the quantity<br />

κ(L) = sup � τ1 ···τd : τi > 0, {x :|x j|

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