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Lookup table. In computer science, a lookup table ( LUT) is an array that replaces runtime computation with a simpler array indexing operation, in a process termed as direct addressing. The savings in processing time can be significant, because retrieving a value from memory is often faster than carrying out an "expensive" computation or input ...
Combinations and permutations in the mathematical sense are described in several articles. Described together, in-depth: Twelvefold way. Explained separately in a more accessible way: Combination. Permutation. For meanings outside of mathematics, please see both words’ disambiguation pages: Combination (disambiguation)
In mathematics, and in particular in combinatorics, the combinatorial number system of degree k (for some positive integer k ), also referred to as combinadics, or the Macaulay representation of an integer, is a correspondence between natural numbers (taken to include 0) N and k - combinations. The combinations are represented as strictly ...
Stars and bars (combinatorics) In the context of combinatorial mathematics, stars and bars (also called "sticks and stones", [ 1] "balls and bars", [ 2] and "dots and dividers" [ 3]) is a graphical aid for deriving certain combinatorial theorems. It can be used to solve many simple counting problems, such as how many ways there are to put n ...
Combination. In mathematics, a combination is a selection of items from a set that has distinct members, such that the order of selection does not matter (unlike permutations ). For example, given three fruits, say an apple, an orange and a pear, there are three combinations of two that can be drawn from this set: an apple and a pear; an apple ...
An archetypal double counting proof is for the well known formula for the number () of k-combinations (i.e., subsets of size k) of an n-element set: = (+) ().Here a direct bijective proof is not possible: because the right-hand side of the identity is a fraction, there is no set obviously counted by it (it even takes some thought to see that the denominator always evenly divides the numerator).
The band gap is called "direct" if the crystal momentum of electrons and holes is the same in both the conduction band and the valence band; an electron can directly emit a photon. In an "indirect" gap, a photon cannot be emitted because the electron must pass through an intermediate state and transfer momentum to the crystal lattice.
Second, medical roots generally go together according to language, i.e., Greek prefixes occur with Greek suffixes and Latin prefixes with Latin suffixes. Although international scientific vocabulary is not stringent about segregating combining forms of different languages, it is advisable when coining new words not to mix different lingual roots.