# summing+up

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**Mathematics of Sudoku**— The class of Sudoku puzzles consists of a partially completed row column grid of cells partitioned into N regions each of size N cells, to be filled in using a prescribed set of N distinct symbols (typically the numbers {1, ..., N}), so that each …122

**Character sum**— In mathematics, a character sum is a sum of values of a Dirichlet character χ modulo N, taken over a given range of values of n. Such sums are basic in a number of questions, for example in the distribution of quadratic residues, and in… …123

**Open collector**— A simple schematic of an open collector of an integrated circuit (IC). An open collector is a common type of output found on many integrated circuits (IC). Instead of outputting a signal of a specific voltage or current, the output signal is… …124

**Midy's theorem**— In mathematics, Midy s theorem, named after French mathematician E. Midy,[1] is a statement about the decimal expansion of fractions a/p where p is a prime and a/p has a repeating decimal expansion with an even period. If the period of the… …125

**Vertex model**— A vertex model is a type of statistical mechanics model in which the Boltzmann weights are associated with a vertex in the model (representing an atom or particle). This contrasts with a nearest neighbour model, such as the Ising model, in which… …126

**Square-lattice Ising model**— The two dimensional square lattice Ising model was solved by Lars Onsager in 1944 for the special case that the external field H = 0. The general case for H eq 0 has yet to be found.Consider the 2D Ising model on a square lattice Lambda with N… …127

**Michael John Smith (espionage)**— For other people named Michael Smith, see Michael Smith (disambiguation). Michael John Smith was born on 22 September 1948. He was charged in the UK with four offences under sections 1(1)(b) and (c) the Official Secrets Act 1911 in 1992 and… …128

**Buchla 200e**— The Buchla 200e is a modular analog synthesizer designed by electronic music pioneer Don Buchla and built by Buchla and Associates. Modules 200e synthesizer platform includes several modules that roughly correspond to the canonical analog… …