What is Linear operator: Definition and 117 Discussions

In mathematics, a linear map (also called a linear mapping, linear transformation, vector space homomorphism, or in some contexts linear function) is a mapping



V

W


{\displaystyle V\to W}
between two vector spaces that preserves the operations of vector addition and scalar multiplication. The same names and the same definition are also used for the more general case of modules over a ring; see Module homomorphism.
If a linear map is a bijection then it is called a linear isomorphism. In the case where



V
=
W


{\displaystyle V=W}
, a linear map is called a (linear) endomorphism. Sometimes the term linear operator refers to this case, but the term "linear operator" can have different meanings for different conventions: for example, it can be used to emphasize that



V


{\displaystyle V}
and



W


{\displaystyle W}
are real vector spaces (not necessarily with



V
=
W


{\displaystyle V=W}
), or it can be used to emphasize that



V


{\displaystyle V}
is a function space, which is a common convention in functional analysis. Sometimes the term linear function has the same meaning as linear map, while in analysis it does not.
A linear map from V to W always maps the origin of V to the origin of W. Moreover, it maps linear subspaces in V onto linear subspaces in W (possibly of a lower dimension); for example, it maps a plane through the origin in V to either a plane through the origin in W, a line through the origin in W, or just the origin in W. Linear maps can often be represented as matrices, and simple examples include rotation and reflection linear transformations.
In the language of category theory, linear maps are the morphisms of vector spaces.

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  1. F

    Matrix of. Linear operator question

    I am trying to figure out what the matrix of this linear operator would be: T:M →AMB where A, M, B are all 2X2 matrices with respect to the standard bases of a 2x2 matrix viz. e11, e12 e21 and e22. Any ideas? Il know it should be 2X8 matrix. I am trying to teach myself Abstract algebra using...
  2. F

    Linearly independent sets within repeated powers of a linear operator

    Homework Statement Suppose that T:W -> W is a linear transformation such that Tm+1 = 0 but Tm ≠ 0. Suppose that {w1, ... , wp} is basis for Tm(W) and Tm(uk) = wk, for 1 ≤ k ≤ p. Prove that {Ti(uk) : 0 ≤ i ≤ m, 1 ≤ j ≤ p} is a linearly independent set.Homework Equations The Attempt at a Solution...
  3. D

    Linear operator exercise i can't understand

    Homework Statement Let x=(x1,x2,x3), Ax:=(x2-x3,x1,x1+x3), Bx:=(x2,2x3,x1) Find: (3B+2A2)x. Homework Equations The Attempt at a Solution Warning: I have no idea what I'm doing! (3B+2A2)x = 3Bx+2A2x 3Bx = (3x2,6x3,3x1) Now to find 2A2x. Considering that an index has a...
  4. S

    What symbol is used for linear operator actions?

    Given a vector v\in H: R2->R3 which is a function from R2 to R3, and an operator G: H->H on the space H in which v lives, what is the most commonly used symbol to refer to this mapping, i.e., G(v)=G\otimes v or something else?
  5. S

    Showing a linear operator is compact

    Homework Statement Let [e_{j}:j\in N] be an orthonormal set in a Hilbert space H and \lambda_{k} \in R with \lambda_{k} \rightarrow 0 Then show that Ax=\sum_{j=1}^{\infty} \lambda_{j}(x,e_{j})e_{j} Defines a compact self adjoint operator H \rightarrow H The Attempt at a Solution...
  6. S

    Showing that the range of a linear operator is not necessarily closed

    Homework Statement Let T: \ell^{2} \rightarrow \ell be defined by T(x)=x_{1},\frac{1}{2}x_{2},\frac{1}{3}x_{3},\frac{1}{4}x_{4},...} Show that the range of T is not closed The Attempt at a Solution I figure that I need to find some sequence of x_{n} \rightarrow x such that...
  7. Shackleford

    Proving the Bi-Implication of Inner Product and Norm in Linear Operators

    I don't know how to start this problem. Since it's a bi-implication, I need to show each statement implies the other. I started playing around with the definitions of inner product and norm directly, but it's not going anywhere...
  8. H

    Adjoint of linear Operator and T-invariant subspace

    Homework Statement Let T be a linear operator on an inner product space V and W be a T-invariant subspace of V. If W is both T and T* invariant, prove that (T_{W})* = (T*)_{W}. Note that T_{W} denotes the restriction of T to W Homework Equations \forallx\inW, T_{W}(x) = T(x)...
  9. H

    Is T a One-to-One Linear Operator?

    Homework Statement Let T be a linear operator on a finite dimensional vector space V. Suppose ||T(x)|| = ||x|| for all x in V, prove that T is one to one. Homework Equations ||T(x)||^2 = <T(x),T(x)> ||x||^2 = <x,x> The Attempt at a Solution Suppose T(x) = T(y) x, y in V Then...
  10. jinksys

    Verify that any square matrix is a linear operator when considered as a linear map.

    Homework Statement Verify that any square matrix is a linear operator when considered as a linear transformation. Homework Equations The Attempt at a Solution If a square matrix A\inℂ^{n,n} is a linear operator on the vector space C^{n}, where n ≥ 1, then the square matrix A is...
  11. H

    Find Linear operator [L] and compute

    Homework Statement Let L be a linear operator such that: L[1, 1, 1, 1] = [2, 1, 0, 0] L[1, 1, 1, 0] = [0, 2, 1, 0] L[1, 1, 0, 1] = [1, 2, 0, 0] L[1, 0, 1, 1] = [2, 1, 0, 1] a) Find [L] b) Compute L[1, 2, 3, 4] Homework Equations The Attempt at a Solution I used another...
  12. F

    Row reducing the matrix of a linear operator

    I'm having difficulty understanding the concepts presented in the following question. I'm given a matrix, [2,4,1,2,6; 1,2,1,0,1; ,-1,-2,-2,3,6; 1,2,-1,5,12], which is the matrix representation of a linear operator from R5 to R4. The question asks me to find a basis of the image and the...
  13. F

    Matrix Representation of a linear operator

    T is a linear operator from the space of 2 by 2 matrices over the complex plane to the complex plane, that is T: mat(2x2,C)\rightarrowC, given by T[a b; c d] = a + d T operates on a 2 by 2 matrix with elements a, b, c, d, in case that isn't entirely clear. So T gives the trace of the...
  14. H

    Is L(A) = P^-1AP an Invertible Linear Operator?

    Let P belongs to Mnn be a nonsingular matrix and Let L:Mnn>>>Mnn be given by L(A) = P^-1AP for all A in Mnn. Prove that L is an invertible linear operator. I have no clues how to start this question. What do I need to prove for this question? and why
  15. P

    Diagonisability of a linear operator

    Homework Statement Let T be a linear operator on a vector space V,and let W be a T-invariant subspace of V.Define \ddot{T}:V⁄W→V⁄W by \ddot{T}(v+W)=T(v)+W for any v+W∈V⁄W. Prove that if both TW and \ddot{T} are diagonisable and have no common eigenvalues, then T is diagonisable. Homework...
  16. Q

    Matrix Representation of Nilpotent Linear Operator

    Homework Statement (5.5)V = Z_{\xi_{1}} \oplus Z_{\xi_{2}} \oplus ... \oplus Z_{\xi_{k}}, the basis for V is: \xi_{1}, \eta(\xi_{1}), ..., \eta(\xi_{1})^{p_{1} - 1} \xi_{2}, \eta(\xi_{2}), ..., \eta(\xi_{2})^{p_{2} - 1} . . . \xi_{k}, \eta(\xi_{k}), ..., \eta_(\xi_{k})^{p_{k} - 1}...
  17. B

    Calculating Representation of Linear Operator for Symmetric Matrix

    Homework Statement Let L(x) a linear operator defined by setting the diagonal elements of x to zero. What will be the representation of this operator to the following basis set? x E X. X denote the set of all real symmetric 3x3 matrices. Homework Equations L*y=x L=x*inv(y)...
  18. P

    Spectra of T and T* when T is a bounded linear operator

    Hi, If T is a bounded linear operator on a Hilbert space, what can we say about the spectra of T and T* (\sigma(T)=\{\lambda:T-\lambda I is not invertible})?
  19. M

    Linear operator on Hilbert space with empty spectrum

    Homework Statement Much as the title says, I need to construct an example of a linear operator on Hilbert space with empty spectrum. I can very easily construct an example with empty point-spectrum (e.g. the right-shift operator on l_2), but this has very far from empty spectrum. If I...
  20. P

    Testing Change of Basis in Linear Operator

    I just want to test/verify my knowledge of change of basis in a linear operator.. (it's not a homework question). Suppose I have linear operator mapping R^2 into R^2, and expressed in the canonical basis (1,0), (0,1). Suppose (for the sake of discussion) that the linear operator is given by...
  21. D

    Injectivity of a linear operator

    Technically this isn't homework, but just something I saw another user state without proof in a very different thread. I believe, however, that it is specific enough to pass as a "homework question" so I thought I'd pretend that it was and post it here, because I'm getting a bit frustrated with...
  22. W

    The Adjoint of a Linear Operator: When is ||T(x)|| equal to ||x||?

    Homework Statement Let T be a linear operator on an inner product space V. Prove that ||T(x)|| = ||x|| for all xεV iff <T(x),T(y)> = <x,y> for all x,yεV Homework Equations The Attempt at a Solution <T(x),T(y)> = <x,y> so <x,T^*T(y)> =<x,y> This seems too simple. What...
  23. D

    Decomposition of linear operator

    Homework Statement Show that any linear operator \hat{O} can be decomposed as \hat{O}=\hat{O}'+i\hat{O}'', where \hat{O}' and \hat{O}'' are Hermitian operators. Homework Equations Operator is Hermitian if: T=T^{\dagger}The Attempt at a Solution I don't know where to start :\ Should I try...
  24. clope023

    Linear operator on the set of polynomials

    Homework Statement Let L be the operator on P_3(x) defined by L(p(x)) = xp'(x)+p"(x) if p(x) = a_0(x)+a_1(x)+a_2(1+x^2) calculate L^n(p(x)) Homework Equations stuck between 2 possible solutions i) as powers of x decrease the derivatives of p(x) increase ii) as derivatives...
  25. L

    How Does the Circle Group Influence Linear Transformations in a Sin-Cos Basis?

    I have been re-reading some linear analysis the last week, and I have been playing around a bit with the linear subspace of \mathbb{R}^\mathbb{R} that you get with the basis {sin x, cos x}. It didn't take me long to realize that the family of transformations parametrized by theta T_\theta ...
  26. G

    Linear Operator such that it is Zero Operator

    Homework Statement Let T, linear operator on non fin. dim. Vector Space over field of complex numbers such that there exists T*, adjoint of T. If <T(x),x> = 0 for all x in V then T=T_0 T_0 s.t. T_0(x)=0 for all x in V 2. The attempt at a solution Consider <T(x''),x''> s.t. x''=x' + y...
  27. T

    What is the adjoint linear operator and how do you find it?

    If L is the following first-order linear differential operator L = p(x) d/dx then determine the adjoint operator L* such that integral from (a to b) [uL*(v) − vL(u)] dx = B(x) |from b to a| What is B(x)? sorry.. on my book there's only self-adjointness i don't quiet understand what is...
  28. R

    What is the Adjoint of a Linear Operator?

    Homework Statement T is a linear operator on a finite dimensional vector space. then N(T*T)=N(T). the null space are equal. Homework Equations The Attempt at a Solution this is my method, but its does not work if dim(R(T))=0. I'm only concerned with showing N(T*T) \subseteq...
  29. T

    Questioning the Invertibility of a Linear Operator T

    I have a question about the invertibility of a linear operator T. In Friedberg's book, Theorem 6.18 (c) claims that if B is an orthonormal basis for a finite-dimensional inner product space V, then T(B) is an orthonromal basis for V. I don't understand the proof, I think the book only...
  30. mnb96

    Is convolution a linear operator?

    Hello, If f is a morphism between two vector spaces, we say it is linear if we have: 1) f(x+y) = f(x) + f(y) 2) f(ax) = af(x) Now, if f is the convolution operator \ast , we have a binary operation, because convolution is only defined between two functions. Can we still talk about linearity in...
  31. C

    Linear Operator and Self Adjoint

    I would be grateful for some help/tips/with this question. Let (V,<,>) be a complex inner product space with an orthonormal basis {v1,v2,...vn}. Let L:V------>V be a linear operator. Explain what is meant by saying that L is self-adjoint. Let A=a_ij be the matrix representing L with respect...
  32. G

    When Do Similar Linear Operators Share Ordered Bases?

    Homework Statement Let V be a finite-dimensional vector space over the field F and let S and T be linear operators on V. We ask: When do there exist ordered bases a and b for V such that [S]a = [T]b? Prove that such bases exist if and only if there is an invertible linear operator U on V...
  33. G

    Proving Disjoint Range & Null Space of Linear Operator T

    Homework Statement Given a linear operator T, show that if rank(T^2)=rank(T), then the range and null space are disjoint. So I know that I can form a the same basis for range(T^2) and range(T), but I'm not sure where to go from there.
  34. Y

    Must every linear operator have eigenvalues? If so, why?

    It seems to me that http://en.wikipedia.org/wiki/Schur_decomposition" relies on the fact that every linear operator must have at least one eigenvalue...but how do we know this is true? I have yet to find a linear operator without eigenvalues, so I believe every linear operator does have at...
  35. E

    Functional Analysis, Show that the range of a bounded linear operator

    Homework Statement Show that the range \mathcal{R}(T) of a bounded linear operator T: X \rightarrow Y is not necessarily closed. Hint: Use the linear bounded operator T: l^{\infty} \rightarrow l^{\infty} defined by (\eta_{j}) = T x, \eta_{j} = \xi_{j}/j, x = (\xi_{j}). Homework Equations...
  36. J

    A linear operator T on a finite-dimensional vector space

    Definitions: A linear operator T on a finite-dimensional vector space V is called diagonalizable if there is an ordered basis B for V such that [T]_B is a diagonal matrix. A square matrix A is called diagonalizable if L_A is diagonalizable. We want to determine when a linear operator T on a...
  37. P

    Linear Algebra, Adjoint of a Linear Operator and Inner Product Spaces

    Homework Statement For each of the following inner product spaces V (over F) and linear transformation g:=V \rightarrow F, find a vector y such that g(x) = <x,y> for all x element of V. The particular case I'm having trouble with is: V=P2(R), with <f,h>=\int_0^{1} f(t)h(t)dt ...
  38. J

    Kernel of the adjoint of a linear operator

    Homework Statement Let V be an inner product space and T:V->V a linear operator. Prove that if T is normal, then T and T* have the same kernel (T* is the adjoint of T). Homework Equations The Attempt at a Solution Let us assume x is in the kernel of T. Then, TT*x =T*Tx = T*0= 0...
  39. S

    A question about the rank of a linear operator

    Let T is a linear transformation from a vector space V to V itself. The dimension of V, denoted by dim(V), is finite. If the rank of T, denoted by rk(T), is equivalent to the rank of TT, i.e., rk(T)=rk(TT) why is the intersection of image of T(denoted by im(T)) and the kernel of T(denoted...
  40. N

    What Are the Spectral Properties of the Multiplication Operator M_phi?

    Homework Statement Let 1 \leq p \leq \infty and let (X,\Omega, \mu) be a \sigma-finite measure space. For \phi \in L^\infty(\mu) , define M_\phi on L^p(\mu) by M_\phi f = \phi f \forall f \in L^(X,\Omega,\mu). I need to find the following: \sigma(M_\phi) , \sigma_ap(M_\phi), and...
  41. T

    Prove that its a linear operator

    prove that a linear operator.. T(f):=\frac{\mathrm{d^2f} }{\mathrm{d} x^2}+2\frac{\mathrm{df} }{\mathrm{d} x} T(kf)=kT(f) part: T(kf):=k\frac{\mathrm{d^2f} }{\mathrm{d} x^2}+2k\frac{\mathrm{df} }{\mathrm{d} x}=k(\frac{\mathrm{d^2f} }{\mathrm{d} x^2}+2\frac{\mathrm{df} }{\mathrm{d}...
  42. S

    Can a Linear Operator Satisfying A^2 - A + I = 0 Always Have an Inverse?

    Homework Statement Show that if an operator A satisfies A2 - A + I = 0 then A has an inverse. Express A-1 as a simple polynomial of A. Homework Equations I'm not sure that this is relevant, but A-1=1/(detA)TrC where TrC is the transpose of the matrix of cofactors. Also: If detA = 0 then the...
  43. T

    Comparing subspaces of a linear operator

    Statement Let S be a linear operator S: U-> U on a finite dimensional vector space U. Prove that Ker(S) = Ker(S^2) if and only if Im(S) = Im(S^2) So, I'm really not sure about how to prove this properly. I have a few ideas, but this one seemed to make sens intuitively to me. So, I'm...
  44. N

    Apparent fallacy in linear operator theory

    Butkov's book present the theory of linear operators this way: Suppose a linear operator \alpha transforms a basis vector \hat{\ e_i} into some vector \hat{\ a_i}.That is we have \alpha\hat{\ e_i}=\hat{\ a_i}......(A) Now the vectors \hat{\ a_i} can be represented by its co-ordinates...
  45. M

    Spectral Decomposition of Linear Operator T

    [b]1. Let T be the linear operator on R^n that has the given matrix A relative to the standard basis. Find the spectral decomposition of T. A= 7, 3, 3, 2 0, 1, 2,-4 -8,-4,-5,0 2, 1, 2, 3 [b]3. eigen values are 1 (mulitplicity 1), -1 (mult. 1), 3 (mult. 2). And associated eigen...
  46. B

    Vector space, basis, linear operator

    Homework Statement Let V be a vector space of dimension n. And the linear operators E=A^0, A^1, A^2, ... A^(n-1) are linearly independent. Prove that there exists a v in V such that V=<v, Av, A^2v, ..., A^(n-1)v> Homework Equations The Attempt at a Solution Here are something that...
  47. B

    An equation related to the dimension of linear operator

    Homework Statement Let V be a finite vector space, and A, B be any two linear operator. Prove that, rank A = rank B + dim(Im A \cap Ker B) The Attempt at a Solution Since rank A = dim I am A dim(Im B)+ dim(Ker B)=dim V dim(Im A + Ker B)=dim(Im A)+dim(Ker B)-dim(Im A \cap Ker B) It...
  48. D

    Induction and Fundamental Theorem of Calculus for Bounded Linear Operators

    Homework Statement http://img389.imageshack.us/img389/9272/33055553mf5.png The Attempt at a Solution Via induction: for n=1 equality holds now assume that Vn=Jn. I introduce a dummy variable b and the fundamental theorem of calculus and change order of integration: V_{n+1}f(t)...
  49. D

    Linear Operator Matrix for T Defined by Formula | Example Included

    Greetings, can someone check if I'm doing this correctly? I have to find the standard matrix for the linear operator T defined by the formula. For example, T(x1,x2,x3) = (x1 + 2x2 + x3, x1+ 5x2, x3) Is the matrix I want just simply, T = 1 2 1 1 5 0 0 0 1 I'm basing this...
  50. W

    Proof that linear operator has no square root

    Homework Statement Suppose T \in L(\textbf{C}^3) defined by T(z_{1}, z_{2}, z_{3}) = (z_{2}, z_{3}, 0). Prove that T has no square root. More precisely, prove that there does not exist S \in L(\textbf{C}^3) such that S^{2} = T. Homework EquationsThe Attempt at a Solution I showed in a...
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