Spectral theorem: Difference between revisions

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m Hermitian maps and Hermitian matrices: solutions to ->roots of (relating to the characteristic polynomial)
Hermitian maps and Hermitian matrices: Rephrased; getting a diagonal matrix is not dependent on having the eigenvector basis be orthonormal
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The spectral theorem holds also for symmetric maps on finite-dimensional real inner product spaces, but the existence of an eigenvector does not follow immediately from the [[fundamental theorem of algebra]]. To prove this, consider {{math|''A''}} as a Hermitian matrix and use the fact that all eigenvalues of a Hermitian matrix are real.
 
IfThe onematrix chooses the eigenvectorsrepresentation of {{math|''A''}} asin an orthonormala basis of eigenvectors is diagonal, and by the matrixconstruction representationthe proof gives a basis of {{math|''A''}}mutually inorthogonal thiseigenvectors; by choosing them to be unit vectors one obtains an orthonormal basis isof diagonaleigenvectors. Equivalently, {{math|''A''}} can be written as a linear combination of pairwise orthogonal projections, called its '''spectral decomposition'''. Let
 
:<math> V_\lambda = \{\,v \in V: A v = \lambda v\,\}</math>