Tuesday 8 October 2013

Inner Product Spaces

Inner product- Let F be the field of real or Complex numbers and V vector space over F. An inner product on V is a fuction which assigns to each ordered pair of vectors α ,β ∈ V a scalar (α/β) ∈ F, defined as
             For α ,β , γ ∈ V, and all scalars C
            (a) (α + β/γ) = (α/γ) + (β/γ)
            (b) (cα/β) = c(α/β)
            (c) (β/α) = (α̅/̅β̅) (a complex conjugate)
            (d) (α/α) > 0 if α ≠ 0.

Inner product spaces- An inner product space is a real or complex space with a specified inner product on that space.


Norm- If ||α||(α/α), then ||α|| is called norm of (α/α).


Euclidean space- A finite dimensional real inner product space.


Unitary space- A complex inner product space.


Orthogonal set- Let α and β be vectors in an inner product space V. Then α is orthogonal to β if  (α/β) = 0.


Orthonormal set- The orthogonal set S, with property ||α|| = 1, α∈S.


Orthogonal complement- Let V be a inner product space and SV. The othogonal complement of S is the set S of all vectors in V which are orthogonal to every vector in S.


T preserves inner product- Let V and W be inner product spaces over the same field and T be a linear transformation from V into W. We say T preserves inner products if 
(Tα/Tβ) = (α/β) for all α,β  V.

Isomorphism- An isomorphism of V onto W is a vector space isomorphism T of V onto W, whick also preserves inner product,

i.e., (Tα/Tβ) = (α/β) for all α,β  V.

Unitary operator- A unitary operator on an inner product space is an isomorphism of the space onto itself.


Unitary matrix- A complex square matrix A is unitary if A*A = I.


Orthogonal matrix- A real or complex square matrix A is orthogonal if ATA = I.


Unitary equivalent- If A and B are complex n×matrices then B is unitarily equivalent to A if there exist unitary matrix P of order  n×: B = P-1AP.


Orthogonally equivalent- If A and B are complex matrices then B is orthogonally equivalent to A if there exist orthogonal matrix P of order n×: B = P-1AP.


Normal Operators:
Let V ne a finite dimensional inner product space and T is linear operator on V. Then T is normal if TT* = T*T.

Normal matrix- A complex n×matrix A is called normal if AA* = A*A.

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