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  2. Raising and lowering indices - Wikipedia

    en.wikipedia.org/wiki/Raising_and_lowering_indices

    It is common convention to use greek indices when writing expressions involving tensors in Minkowski space, while Latin indices are reserved for Euclidean space. Well-formulated expressions are constrained by the rules of Einstein summation: any index may appear at most twice and furthermore a raised index must contract with a lowered index ...

  3. Ricci calculus - Wikipedia

    en.wikipedia.org/wiki/Ricci_calculus

    Each index has one possible value per dimension of the underlying vector space. The number of indices equals the degree (or order) of the tensor. For compactness and convenience, the Ricci calculus incorporates Einstein notation, which implies summation over indices repeated within a term and universal quantification over free indices ...

  4. Einstein notation - Wikipedia

    en.wikipedia.org/wiki/Einstein_notation

    An index that is summed over is a summation index, in this case "i ". It is also called a dummy index since any symbol can replace "i " without changing the meaning of the expression (provided that it does not collide with other index symbols in the same term). An index that is not summed over is a free index and should appear only once per ...

  5. Frobenius method - Wikipedia

    en.wikipedia.org/wiki/Frobenius_method

    Some solutions of a differential equation having a regular singular point with indicial roots = and .. In mathematics, the method of Frobenius, named after Ferdinand Georg Frobenius, is a way to find an infinite series solution for a linear second-order ordinary differential equation of the form ″ + ′ + = with ′ and ″.

  6. Fredholm operator - Wikipedia

    en.wikipedia.org/wiki/Fredholm_operator

    In mathematics, Fredholm operators are certain operators that arise in the Fredholm theory of integral equations.They are named in honour of Erik Ivar Fredholm.By definition, a Fredholm operator is a bounded linear operator T : X → Y between two Banach spaces with finite-dimensional kernel ⁡ and finite-dimensional (algebraic) cokernel ⁡ = / ⁡, and with closed range ⁡.

  7. Open Problems in Mathematics - Wikipedia

    en.wikipedia.org/wiki/Open_Problems_in...

    Open Problems in Mathematics is a book, edited by John Forbes Nash Jr. and Michael Th. Rassias, published in 2016 by Springer (ISBN 978-3-319-32160-8). The book consists of seventeen expository articles, written by outstanding researchers, on some of the central open problems in the field of mathematics.

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  9. 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]