Bloch wave – MoM method the wave numbers in any of the 3 periodic coordinate directions. This can happen for example when the free space wavelength exactly equals the lattice spacing. This is a statistically rare occurrence in computational practice and corresponds to a propagation anomaly similar to a Wood's reflection anomaly for gratings. To compute bands of the crystal (i.e. "k"-"k" diagrams), successive values of frequency ("k") are tried - in conjunction with pre-selected values of propagation constant ("k") and propagation direction (θ & φ) - until a combination is found which drives the determinant of the matrix to zero. Equation (4.2) has been
Distance oracle auxiliary data structure. A simple data structure that achieves this goal is a "matrix" which specifies, for each pair of nodes, the distance between them. This structure allows us to answer queries in constant time formula_2, but requires formula_3 extra space. It can be initialized in time formula_4 using an all-pairs shortest paths algorithm, such as the Floyd–Warshall algorithm. A DO lies between these two extremes. It uses less than formula_3 space in order to answer queries in less than formula_1 time. Most DOs have to compromise on accuracy, i.e. they don't return the accurate distance but rather a constant-factor