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  2. Index notation - Wikipedia

    en.wikipedia.org/wiki/Index_notation

    A vector treated as an array of numbers by writing as a row vector or column vector (whichever is used depends on convenience or context): = (), = Index notation allows indication of the elements of the array by simply writing a i, where the index i is known to run from 1 to n, because of n-dimensions. [1]

  3. Raising and lowering indices - Wikipedia

    en.wikipedia.org/wiki/Raising_and_lowering_indices

    By being non-degenerate we mean that for each such that , there is a such that ϕ ( v , u ) ≠ 0. {\displaystyle \phi (v,u)\neq 0.} In concrete applications, ϕ {\displaystyle \phi } is often considered a structure on the vector space, for example an inner product or more generally a metric tensor which is allowed to have indefinite signature ...

  4. Ricci calculus - Wikipedia

    en.wikipedia.org/wiki/Ricci_calculus

    Ricci calculus, and index notation more generally, distinguishes between lower indices (subscripts) and upper indices (superscripts); the latter are not exponents, even though they may look as such to the reader only familiar with other parts of mathematics.

  5. Einstein notation - Wikipedia

    en.wikipedia.org/wiki/Einstein_notation

    In mathematics, especially the usage of linear algebra in mathematical physics and differential geometry, Einstein notation (also known as the Einstein summation convention or Einstein summation notation) is a notational convention that implies summation over a set of indexed terms in a formula, thus achieving brevity.

  6. Index (statistics) - Wikipedia

    en.wikipedia.org/wiki/Index_(statistics)

    Sample of a well maintained data [clarification needed]. In statistics and research design, an index is a composite statistic – a measure of changes in a representative group of individual data points, or in other words, a compound measure that aggregates multiple indicators.

  7. Index of a subgroup - Wikipedia

    en.wikipedia.org/wiki/Index_of_a_subgroup

    and further, G does not act on this geometry, nor does it reflect any of the non-abelian structure (in both cases because the quotient is abelian). However, it is an elementary result, which can be seen concretely as follows: the set of normal subgroups of a given index p form a projective space, namely the projective space

  8. Index set - Wikipedia

    en.wikipedia.org/wiki/Index_set

    In mathematics, an index set is a set whose members label (or index) members of another set. [1] [2] For instance, if the elements of a set A may be indexed or labeled by means of the elements of a set J, then J is an index set.

  9. Matrix (mathematics) - Wikipedia

    en.wikipedia.org/wiki/Matrix_(mathematics)

    According to some authors, a principal submatrix is a submatrix in which the set of row indices that remain is the same as the set of column indices that remain. [ 18 ] [ 19 ] Other authors define a principal submatrix as one in which the first k rows and columns, for some number k , are the ones that remain; [ 20 ] this type of submatrix has ...