Linear algebra is concerned with vector spaces of all dimensions and linear transformations between them, including systems of linear equations, bases, dimensions, subspaces, matrices, determinants, traces, eigenvalues and eigenvectors, diagonalization, Jordan forms, etc. For questions specifically ...

learn more… | top users | synonyms

1
vote
0answers
9 views

Warm start of simplex algorithm after update of constraint matrix

Assume we found an optimal solution $\mathbf{x}_1$ of the linear program \begin{gather} \max \mathbf{n}^T\mathbf{x}\mbox{ s.t. }A\mathbf{x} \leq \mathbf{b}\tag{1} \end{gather} using the simplex ...
1
vote
0answers
6 views

About the algebra used in linear discriminant analysis in scikit learn (LDA using SVD)

I've looked for info about how LDA is impemented in scikit-learn but there's no clue about what I'm looking for. In this code in python: ...
0
votes
0answers
7 views

Probability That a Polynomial has Specific Root when we use Permutation Polynomial

To some extent similar question was asked here: Polynomial Interpolation and Security Imagine we have $\vec{x}=(x_1,...x_n)$ and two polynomials $P_1$ and $P_2$. Degree of $P_1$ is fixed $n-2$, ...
0
votes
0answers
17 views

Write down the 5 equations Cx = b. Find a combination of left sides that gives zero(5x5 matrix)? [on hold]

The very last words say that the 5 by 5 centered difference matrix is not invertible. Write down the 5 equations Cx = b. Find a combination of left sides that gives zero. What combination of b1, b2, ...
0
votes
1answer
32 views

Eigen values of A*A are non negatives.

If $A$ is a complex matrix of order $n$ then i like to prove that all eigen values of $A*A$ are non negative where $*$ is transpose conjugate . $ \lambda \|x\|^2 = \langle \lambda x,x \rangle = ...
1
vote
1answer
19 views

Boundedness of matrix norm

Let $A$ be a n by n matrix whose entries are continuous functions of $x\in \mathbb{R}^n$. Fix a matrix norm $\|\cdot \|$ and assume that $\|A(x^\star)\| < 1$. Then, the claim is that there exists ...
1
vote
2answers
15 views

$W$ a subset of $\mathbb{R}^5$ consisting of all vectors an odd number of the entries in which are equal to $0$. Is $W$ a subspace of $\mathbb{R}^5$?

Let $W$ be the subset of $\mathbb{R}^5$ consisting of all vectors an odd number of the entries in which are equal to $0$. Is $W$ a subspace of $\mathbb{R}^5$? I'm not sure how to do this. Any ...
2
votes
1answer
22 views

Finding an equilibrium solution to a first order system of equations.

Given a model: $ y''+\alpha y'+\beta y + \gamma y = -g $ I can see that it can be converted to a system of first order equations as follows: $y_{1}=y$, $y_{2}=y'$ and as such $y_{1}'=y'$ and ...
0
votes
0answers
27 views

Let $F$ be the set of all functions of the form $f$: $t\to \sum_{k=1}^n a_k \cos(kt)+b_k \sin(kt)$. Is $F$ an integral domain? Is it a field?

Let $F$ be the set of all functions $f$ from $\mathbb{R}$ to itself of the form $f$: $t\to \sum_{k=1}^n a_k \cos(kt)+b_k \sin(kt)$ where $a_k$ and $b_k$ are real numbers and n is a natural number. ...
0
votes
0answers
5 views

formula to calculate bounding coordinates of an arc in space

I have an arc in space with known 2 endpoints x1,y1 and x2,y2 centrepoint x3,y3 radius r What would be the formula to find the coordinates of a box that fits the limits of the arc.
0
votes
4answers
54 views

Transform $f(x_1,x_2,x_3)=2{x_1}^2+5{x_2}^2+5{x_3}^2+4x_1x_2-4x_1x_3-8x_2x_3$ to a diagonal form.

I try to transform Transform $$f(x_1,x_2,x_3)=2{x_1}^2+5{x_2}^2+5{x_3}^2+4x_1x_2-4x_1x_3-8x_2x_3$$ to a diagonal form. I can do it using eigenvalue, but when I directly complete the square to find its ...
2
votes
1answer
33 views

The norm of a bounded linear operator has this formula: $\|T\| = \sup_{\|v\| = 1} \|T v\|$

Trying to prove $\|T\| = \sup_{\|v\| = 1} \|T v\|$, given $\|T\| := \inf_{C \geq 0} \{C: \|Tv\| \leq C\|v\|\}$. I know that $\|T(v)\| = \|T(\alpha \hat{v})\| \leq C\|\alpha \hat{v}\|$ for $v = ...
2
votes
1answer
29 views

Why is the Span of a subset of a linear space defined in such at way?

If I have a subset $M$ of a linear space $E$, we define the linear span of the subset, $M$, as: $$\operatorname{span} M=\bigcap_\alpha \{E_\alpha : E_\alpha \hookrightarrow E\text{ and } M \subseteq ...
2
votes
2answers
55 views

If $A$ is a $4 \times 4$ matrix with $rank(A) = 1$, then either $A$ is diagonalizable or $A^2 = 0$, but not both

If $A$ is a $4 \times 4$ matrix with rank$(A) = 1$, then either $A$ is diagonalizable (over $C$) or $A^2 = 0$, but not both (Note that $A$ has complex entries) So far, the only thing I've tried ...
2
votes
0answers
40 views

Let the plane V be defined by $ax + by + cz + d = 0$; with $a, b, c, d \in \mathbb{R}$ and the vector $(a; b; c)$ a unit vector.

I am battling to get my mind around some of the concepts involving vectors in $3$-space. This question asks me whether the following statements are True or False: (A) The line $(a; b; c)$ is parallel ...
4
votes
1answer
46 views

$O_{2n}(\mathbb{R}) \cap GL_{n}(\mathbb{C})=U(n)$

During a lecture of a Lie Algebras yesterday, the professor of the class stated the following fact without proof $O_{2n}(\mathbb{R}) \cap GL_{n}(\mathbb{C})=U(n)$ Note that we are viewing ...
0
votes
1answer
22 views

parameterizing two points along a circular path [on hold]

Question: Parameterize points (3, 4) to (-4, 3) along a circular path I know that if I find the vector equation for this it would be r = <3-7t, 4-t>. But I'm not sure what the question is asking ...
0
votes
2answers
57 views

Let $A$ be a $5\times 5$ matrix all of whose eigenvalues are zero. Is $A$ symmetric, anti-symmetric, or $A=-A$?

Let $A$ be a $5\times 5$ matrix all of whose eigenvalues are zero. Which of the following are always true: a. $A=-A$ b. $A^t=-A$ (anti-symmetric) c. $A^t=A$ (symmetric) d. $A^5=0$ For b: ...
1
vote
3answers
38 views

Let $A\in \mathbb C$ be a $2 \times 2$ matrix, let $f(x)=a_0+a_1x+\cdots a_nx^n$ be any polynomial over $\mathbb C$. Comment on $f(A)$

Let $A\in \mathbb C$ be a $2 \times 2$ matrix, let $f(x)=a_0+a_1x+a_2x^2+\cdots a_nx^n$ be any polynomial over $ \mathbb C$. Then which of the following is true? a) $f(A)$ can be written as ...
0
votes
1answer
20 views

Generator operator of $v$?

Let $\text{U}_+$ be an associative $\mathbb{C}$-algebra with two generators $E$, $H$, and one defining relation $HE - EH = 2E$. Let $M$ be an $\text{U}_+$-module. If $v \in M$ is a nonzero eigenvector ...
0
votes
0answers
9 views

Why quadratic forms with the same isotropic cone are proportional?

Let $V$ be a complex space with a quadratic forms $P$, $Q$. Assume that the isotropic cones for $P$ and $Q$ are the same: $$ P^{-1}(0)=Q^{-1}(0). $$ How to check that there is a constant $c\neq 0$ ...
1
vote
0answers
35 views

Diagonalization: Differential Equations

The booking being used for this course is Differential Equations and Dynamical Systems by Lawrence Perko. The problem is as follows: Let the $n\times n$ matrix $A$ have real, distinct ...
0
votes
1answer
30 views

using Cayley Hamilton to find a power of linear transformation

I have reached the the following formula using Cayley Hamilton: $$T^3-2T+2I=0$$ Now I need to find $T^4$ so what I did is $T(T^3-2T+2I=0)\iff T^4-2T^2+2IT=0\iff T^4=2T^2-2IT$ But the answer is ...
2
votes
2answers
37 views

Let $T,S$ be linear transformations, $T:\mathbb R^4 \rightarrow \mathbb R^4$, such that $T^3+3T^2=4I, S=T^4+3T^3-4I$. Comment on S.

Let $T,S$ be linear transformations, $T:\mathbb R^4 \rightarrow \mathbb R^4$, such that $T^3+3T^2=4I, S=T^4+3T^3-4I$. Then S is: one-one but not onto onto but not one one invertible non-invertible ...
1
vote
2answers
58 views

calculating the characteristic polynomial

I have the following matrix: $$A=\begin{pmatrix} -9 & 7 & 4 \\ -9 & 7 & 5\\ -8 & 6 & 2 \end{pmatrix}$$ And I need to find the characteristic polynomial so I use ...
1
vote
1answer
23 views

Uncoupled Linear System: Differential Equations

I'm trying to make sense of a problem I was given in class and I want to know if I am on the right track. The question is as follows: If $\vec{u}(t)$ and $\vec{v}(t)$ are solutions of the linear ...
0
votes
0answers
16 views

Probability that a Polynomial Has Specific Root When $y_i$'s are Not Random.

Imagine we have $\vec{x}=(x_1,...x_n)$ and two polynomials $P_1$ and $P_2$. Degree of $P_1$ is fixed $n-1$, but degree of $P_2$ can be at most $n-1$. $P_1$ has root $\beta$, where $\beta \leftarrow ...
7
votes
3answers
132 views

Prove that $\det(I-CD)=\det(I-DC) $

Let $C$ and $D$ be matrices such that $DC$ and $CD$ are square matrices of the same dimension. How can one prove that $\det(I-CD)=\det(I-DC)$? This is my approach to the question. I am not sure ...
1
vote
0answers
19 views

Measure change/similarity between two affine transformations

I have two affine transformations $A_1$ and $A_2$ consisting only of a rotation matrix $R_i$ and a translation vector $\overrightarrow{t_i}$ (all in 3D space): $$A_i = \left[ \begin{array}{ccc|c} \, ...
3
votes
2answers
32 views

Sum of three cross products is zero.

Let $u,v,w\in \mathbb R^3$. Prove $u \times( v \times w)+v \times( w \times u)+w \times( u \times v) =0$ I guess things would work out if I just expanded as a ton of products. Is there a better way?
1
vote
1answer
28 views

Characteristic polynomial above the complex numbers

I need to find the Characteristic polynomial of $\begin{pmatrix} i+1 & 0 & 0 \\ 0 & 3i-1 & 2-2i\\ 0 & 2-2i & 3i-1 \end{pmatrix}$ I know that there is not ...
0
votes
1answer
4 views

Solving Augmented Matrix Breaking Strict Triangle Form

I'm trying to solve the following system of equations: $ 3x_1 + 2x_2 + x_3 = 0\\ -2x_1 + x_2 -x_3 = 2\\ 2x_1 - x_2 + 2x_3 = -1 $ From which I'm using the augmented matrix: $$ \left[ ...
1
vote
0answers
43 views

Valid Vector Space Proof (given v + w = 0 prove w = -v)

I'm working through Serge Lang's 'Algebra' and my answers to the proof exercise differ from his but reach the same outcome. I'm not sure if my proofs are invalid or if they are a correct alternative ...
-2
votes
1answer
35 views

how many solutions does a 3x3 linear systems have? [on hold]

I just want to know if 3x3 linear systems has no solution, one solution, or two solutions, three solutions or infinitely many.solutions
1
vote
2answers
32 views

proof-similar matrices have the same characteristic polynomial

I have this proof but did not understand the following step: $$ \det(xI - M^{-1} A M)= \det(M^{-1} xI M - M^{-1} A M)$$ The author said in the comments that it is due to "$xM$ commutes with the ...
1
vote
1answer
23 views

Selecting a basis such that the orientation is preserved

I need to map a polygon from a 3D plane to a 2-dimensional basis, do some processing, and project the result back to 3D. The vertices in the polygon is always ordered counterclockwise and this ...
1
vote
1answer
16 views

Determining intersection of kernel and range of a linear operator.

I was posed the following question : If T is a linear operator on vector space V and given that the kernel and range of T are disjoint, ie. they have only the zero vector in their intersection and T ...
0
votes
2answers
50 views

Proof for $V \cong V^{**}$

Theorem: Let $V$ be an vector space. Then the dual space of $V$'s dual space is canonically isomorphic to $V$. I am able to prove that $V$ is a subspace of $V^{**}$, the map ...
1
vote
1answer
22 views

How to find a $3\times 3$ matrix with a certain null space and certain column space

We were asked to Find a $3\times 3$ matrix whose null space is the $x$-axis and whose column space is the $yz$-plane. I was told that the answer is this, but I didn't understand why: ...
-6
votes
0answers
22 views

In vector space why we not take 1.a=a.1 [on hold]

I solve many question which satisfies this condition.I want to answer this
0
votes
1answer
25 views

Is it possible for a matrix to have nullity different from its transpose?

Say I have a $2\times 3$ matrix with $\operatorname{rank}(A)=1$ and $\operatorname{nullity}(A)=2$, i.e. only one pivot point and two free variables in the solution set of this system because we have ...
2
votes
3answers
70 views

If square matrix A satisfying $A^2-4A+4I=0$ does it follow that A is diagonizable?

I am given the following statement and asked to determine whether it is true or false: If A is a n x n matrix, and $A^2-4A+4I=0$, then A is diagonizable. Any help is appreciated, thank you.
3
votes
1answer
30 views

How many numbers between 1 and 10000, inclusive, are multiples of 12 or 20?

I calculated the multiples of 12 and multiples of 20, 833 and 500 respectively. Now I calculated the multiples of 12 * 20 = 240,and as a result have 41. The solution would be 833 + 500-41 = 1292 ...
0
votes
2answers
32 views

Show that the full null space of the matrix A and its column space in the plane 2x+2y - z = 0

Show that the full null space of the matrix A = $\begin{bmatrix} 0&1&5\\ 1&0&0 \\ 2&2&10 \end{bmatrix}$ is the line $\lambda$(0.-5,1), $\lambda \in \mathbb R^3$ and its ...
3
votes
0answers
29 views

Do I have the correct mental map for adjoint operators for inner product spaces?

Let $X$, $Y$ be finite dimensional inner product spaces, let $A: X \to Y$ be a linear operator, let $A^*: Y \to X$ be the adjoint operator to the linear operator, defined using $<y, Ax>_Y = ...
0
votes
1answer
22 views

about scaling property of proximal operator

If the proximal operator of $f(x)$ is $\text{prox}_{\lambda f}(x)$, what about $cf(x)$ and $f(cx)$, c is a scalar. For example, If $f(x) = ||x||_{1}$, $x \in \mathbb{R}^{n}$, how about the proximal ...
2
votes
0answers
29 views

Linear map is diagonalizable iff its adjoint is diagonalizable

Problem Let $V$ be a finite inner product space and let $T:V \to V$ be a linear transformation. Prove that $T$ is diagonalizable if and only if the adjoint transformation $T^{*}$ is diagonalizable. ...
2
votes
2answers
38 views

Index notation interpretation for matrices

I want to understand the how to interpret the matrices which are represented by index notation. Here is my matrix $𝜎_{𝑖𝑗}+𝜎_{π‘–π‘˜}𝑀_{π‘˜π‘—}βˆ’π‘€_{π‘–π‘˜} 𝜎_{π‘˜π‘—}$ All the matrices in the equation ...
1
vote
2answers
38 views

Explicit example of a basis of invertibles for $n\times n$ matrices

Using a topological (+linear algebra) argument, one can establish the existence of a basis spanning any square matrix using invertible matrices ( $span(GL_n (\Bbb{R}))=\mathcal{M}_n (\Bbb{R}) $). But ...
1
vote
0answers
34 views

Least squares solutions of the linear system

I'm doing problems from old exams, and my solutions don't add up with the professor's solution. The problem is as followed: Find all least squares solutions of the linear system. I checked my ...