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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.
The free indices in a tensor expression always appear in the same (upper or lower) position throughout every term, and in a tensor equation the free indices are the same on each side. Dummy indices (which implies a summation over that index) need not be the same, for example:
For example, two numbers can be multiplied just by using a logarithm table and adding. These are often known as logarithmic properties, which are documented in the table below. [ 2 ] The first three operations below assume that x = b c and/or y = b d , so that log b ( x ) = c and log b ( y ) = d .
In the above example, vectors are represented as n × 1 matrices (column vectors), while covectors are represented as 1 × n matrices (row covectors). When using the column vector convention: "Upper indices go up to down; lower indices go left to right." "Covariant tensors are row vectors that have indices that are below (co-row-below)."
For example, / / = / + / = =, meaning (/) =, which is the definition of square root: / =. The definition of exponentiation can be extended in a natural way (preserving the multiplication rule) to define b x {\displaystyle b^{x}} for any positive real base b {\displaystyle b} and any real number exponent x {\displaystyle x} .
So for example if n is 5, the index cannot be 15 even though this divides 5!, because there is no subgroup of order 15 in S 5. In the case of n = 2 this gives the rather obvious result that a subgroup H of index 2 is a normal subgroup, because the normal subgroup of H must have index 2 in G and therefore be identical to H .
Sylvester's law of inertia (quadratic forms) Sylvester–Gallai theorem (plane geometry) Symmetric hypergraph theorem (graph theory) Symphonic theorem (triangle geometry) Synge's theorem (Riemannian geometry) Sz.-Nagy's dilation theorem (operator theory) Szegő limit theorems (mathematical analysis) Szemerédi's theorem (combinatorics)
This article lists mathematical properties and laws of sets, involving the set-theoretic operations of union, intersection, and complementation and the relations of set equality and set inclusion. It also provides systematic procedures for evaluating expressions, and performing calculations, involving these operations and relations.