Invariant theory studies functions and tensors unchanged by a group action. For a linear representation, the polynomial invariant ring records invariant polynomial functions on the representation space. Tensor invariants and commuting algebra actions connect it with Schur–Weyl duality.
Invariant theory is a branch of mathematics, particularly in the fields of algebra, geometry, and representation theory, that studies properties of mathematical objects that remain unchanged (or invariant) under transformations from a certain group. The most common transformations considered are linear transformations, but the theory can also apply to more general transformation groups. Historically, invariant theory originated in the 19th century, with significant contributions from mathematicians such as David Hilbert and Hermann Weyl.
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