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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.
In Einstein notation (implicit summation over repeated index), contravariant components are denoted with upper indices as in = A covector or cotangent vector has components that co-vary with a change of basis in the corresponding (initial) vector space. That is, the components must be transformed by the same matrix as the change of basis matrix ...
In abstract index notation, the EFE reads as follows: + = where is the Einstein tensor, is the cosmological constant, is the metric tensor, is the speed of light in vacuum and is the gravitational constant, which comes from Newton's law of universal gravitation.
Examples: is a model for 3-dimensional space. The metric is equivalent to the standard dot product., =, equivalent to dimensional real space as an inner product space with =. In Euclidean space, raising and lowering is not necessary due to vectors and covector components being the same.
where (g jk) is the inverse of the matrix (g jk), defined as (using the Kronecker delta, and Einstein notation for summation) g ji g ik = δ j k. Although the Christoffel symbols are written in the same notation as tensors with index notation, they do not transform like tensors under a change of coordinates.
In index-free tensor notation, the Levi-Civita symbol is replaced by the concept of the Hodge dual. [citation needed] Summation symbols can be eliminated by using Einstein notation, where an index repeated between two or more terms indicates summation over that index. For example,
A letter written by Albert Einstein in which he writes out his famous E = mc2 equation has sold at auction for more than $1.2 million, about three times more than it was expected to get, Boston ...
For example, the Ricci tensor is a non-metric contraction of the Riemann curvature tensor, and the scalar curvature is the unique metric contraction of the Ricci tensor. One can also view contraction of a tensor field in the context of modules over an appropriate ring of functions on the manifold [ 5 ] or the context of sheaves of modules over ...