Linear algebra | Matrices

Reducing subspace

In linear algebra, a reducing subspace of a linear map from a Hilbert space to itself is an invariant subspace of whose orthogonal complement is also an invariant subspace of That is, and One says that the subspace reduces the map One says that a linear map is reducible if it has a nontrivial reducing subspace. Otherwise one says it is irreducible. If is of finite dimension and is a reducing subspace of the map represented under basis by matrix then can be expressed as the sum where is the matrix of the orthogonal projection from to and is the matrix of the projection onto (Here is the identity matrix.) Furthermore, has an orthonormal basis with a subset that is an orthonormal basis of . If is the transition matrix from to then with respect to the matrix representing is a block-diagonal matrix with where , and (Wikipedia).

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Related pages

Identity matrix | Basis (linear algebra) | Linear map | Dimension (vector space) | Hilbert space | Linear subspace | Linear algebra | Change of basis | Orthonormal basis | Invariant subspace | Orthogonal complement