What is Frobenius: Definition and 105 Discussions

Frobenius is a surname. Notable people with the surname include:

Ferdinand Georg Frobenius (1849–1917), mathematician
Frobenius algebra
Frobenius endomorphism
Frobenius inner product
Frobenius norm
Frobenius method
Frobenius group
Frobenius theorem (differential topology)
Georg Ludwig Frobenius (1566–1645), German publisher
Johannes Frobenius (1460–1527), publisher and printer in Basel
Hieronymus Frobenius (1501–1563), publisher and printer in Basel, son of Johannes
Ambrosius Frobenius (1537–1602), publisher and printer in Basel, son of Hieronymus
Leo Frobenius (1873–1938), ethnographer
Nikolaj Frobenius (born 1965), Norwegian writer and screenwriter
August Sigmund Frobenius (died 1741), German chemist

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  1. cianfa72

    I Frobenius theorem for differential one forms

    Hi, starting from this old PF thread I've some doubts about the Frobenius condition for a differential 1-form ##\omega##, namely that ##d\omega = \omega \wedge \alpha## is actually equivalent to the existence of smooth maps ##f## and ##g## such that ##\omega = fdg##. I found this About...
  2. P

    Solution verification of ODE using Frobenius' method

    I have no problems with solving this exercise, but my solution disagrees slightly with that given in the answers in the back of the book, and I do not know who's correct. First, we rewrite the equation as $$x''+\frac{3}{2t}x'-\frac{(1+t)}{2t^2}x=0.\tag1$$ We recognize that this is so-called...
  3. cianfa72

    I About global inertial frame in GR - revisited

    Hi, reading this old thread I'd like a clarification about the following: Fermi Normal hypersurface at an event on a comoving FLRW worldline is defined by the collection of spacetime orthogonal geodesics. Such geodesics should be spacelike since they are orthogonal to the timelike comoving...
  4. K

    I Derivation for the indicial exponent in the Frobenius method

    I'm reading a book called Asymptotic Methods and Perturbation Theory, and I came across a derivation that I just couldn't follow. Maybe its simple and I am missing something. Equation 3.3.3b below. y(x) takes the form A(x)*(x-x0)^α and A(x) is expanded in a taylor series.
  5. M

    I Integrability of the tautological 1-form

    Apologies for potentially being imprecise and clunky, but I'm trying understand integrability of the following Hamiltonian $$H(x,p)=\langle p,f(x) \rangle$$ on a 2n dimensional vector space $$T^{\ast}\mathcal{M} =\mathbb{R}^{2n}.$$ Clearly this is just the 1-form $$\theta_{(x,p)} =...
  6. H

    Finding 2 solutions of this Bessel's function using a power series

    I have to find 2 solutions of this Bessel's function using a power series. ##x^2 d^2y/dx^2 + x dy/dx+ (x^2 -9/4)y = 0## I'm using Frobenius method. What I did so far I put the function in the standard form and we have a singularity at x=0. Then using ##y(x) = (x-x_0)^p \sum(a_n)(x-x_0)^n##...
  7. cianfa72

    I Global simultaneity surfaces - how to adjust proper time?

    Hi, searching on PF I found this old post Global simultaneity surfaces. I read the book "General Relativity for Mathematicians"- Sachs and Wu section 2.3 - Reference frames (see the page attached). They define a congruence of worldlines as 'proper time synchronizable' iff there exist a...
  8. cianfa72

    I Synchronous Reference Frame: Definition and Usage

    Hi, reading the Landau book 'The Classical theory of Field - vol 2' a doubt arised to me about the definition of synchronous reference system (a.k.a. synchronous coordinate chart). Consider a generic spacetime endowed with a metric ##g_{ab}## and take the (unique) covariant derivative operator...
  9. A

    I Constants at the end of the Frobenius method

    I'm having a hard time grasping the concept of reducing the two recursive relations at the end of the frobenius method. For example, 2xy''+y'+y=0 after going through all the math i get y1(x) = C1[1-x+1/6*x^2-1/90*x^3+...] y2(x) = C2x^1/2[1-1/3*x+1/30*x^2-1/630*x^3+...] I know those are right...
  10. T

    Question about the Frobenius method and Bessel functions

    Homework Statement i have been trying to learn bessel function for some time now but to not much help firstly, i don't even understand why frobenius method works why does adding a factor of x^r help to fix the singularity problem. i saw answers on google like as not all function can be...
  11. S

    I Is the Frobenius Norm a Reliable Indicator of Matrix Conditioning?

    I have calculated that a matrix has a Frobenius norm of 1.45, however I cannot find any text on the web that states whether this is an ill-posed or well-posed indication. Is there a rule for Frobenius norms that directly relates to well- and ill-posed matrices? Thanks
  12. B

    Can ##a_1## and ##a_2## be zero in the Frobenius' method solution for this DE?

    Homework Statement Use Forbenius' method to solve this DE: $$ 5x^2y''+xy'+(x^3-1)y=0$$ Homework Equations Seek power series solution in the form ##y=\sum _{n=0}^{\infty } a_n x^{n+r}##, ##a_0\neq0## The Attempt at a Solution Sub in the ansatz y, get $$ \sum _{n=0}^{\infty...
  13. J

    Finding the singular points for this differential equation

    Homework Statement If d^2/dx^2 + ln(x)y = 0[/B]Homework Equations included in attempt The Attempt at a Solution I was confused as to whether I include the power series for ln(x) in the solution. It makes comparing coefficients very nasty though. Whenever I expand for m=0 for the a0 I end...
  14. C

    I Solution of an ODE in series Frobenius method

    Hi I am supposed to find solution of $$xy''+y'+xy=0$$ but i am left with reversing this equation. i am studying solution of a differential equation by series now and I cannot reverse a series in the form of: $$ J(x)=1-\frac{1}{x^2} +\frac{3x^4}{32} - \frac{5x^6}{576} ...$$ $$...
  15. Math Amateur

    MHB Frobenius Theorem - Bresar, Theorem 1.4 ....

    I am reading Matej Bresar's book, "Introduction to Noncommutative Algebra" and am currently focussed on Chapter 1: Finite Dimensional Division Algebras ... ... I need help with some aspects of the proof of Theorem 1.4 ... ... Theorem 1.4 reads as follows: Questions 1(a) and 1(b) In...
  16. Math Amateur

    I Frobenius Theorem - Bresar, Theorem 1.4 ....

    I am reading Matej Bresar's book, "Introduction to Noncommutative Algebra" and am currently focussed on Chapter 1: Finite Dimensional Division Algebras ... ... I need help with some aspects of the proof of Theorem 1.4 ... ... Theorem 1.4 reads as follows: Questions 1(a) and 1(b) In the above...
  17. ognik

    MHB Another Frobenius method ODE

    Frobenius method - recurrance relation question If, using the Frobenius method, I get a 3 term recurrence relation of the form $a_{j+2} = a_j .f(k,j) + a_{j-2}. g(k,j)$ ( j even), how do I treat the $a_{j-2}$ term at first? I have found $a_1 = 0$, but how do I find a value for $a_{-2}$ so as...
  18. T

    Quick question about method of Frobenius

    So, when you use the Frobenius method on a differential equation, you assume a solution Σa_k*x^(k+s). Sometimes you get more than one solution for s in the indicial equation. Is the sum of these two solutions you get from evaluating the rest of the problem with each s solution the...
  19. P

    Frobenius Method When Initial Value of A Sum is not 1

    Homework Statement Solve \begin{equation*} 36x^2y''+(5-9x^2)y=0 \end{equation*} using the Frobenius method Homework Equations Assume a solution of the form \begin{equation*} y=\sum_{n=0}^{\infty}{a_nx^{n+s}} \end{equation*} then \begin{equation*}...
  20. W

    Series solution of ODE near singular points with trig

    Homework Statement Given the differential equation (\sin x)y'' + xy' + (x - \frac{1}{2})y = 0 a) Determine all the regular singular points of the equation b) Determine the indicial equation corresponding to each regular point c) Determine the form of the two linearly independent solutions...
  21. B

    Method of Frobenius and indicial equations

    Homework Statement Hello all, I have a quick question, I'm solving a d.e using the Frobenius method and I have the indicial equation: C1(2r-1)(r-1)+C2x(r)(2r+1)=0 Where c1 and c2 are arbitrary constants not equal to zero. Homework EquationsThe Attempt at a Solution My question is, what are...
  22. G

    Frobenius Solution to 2xy'' +5y' -4xy = 0 at x = 0

    After determining that x = 0 is a regular singular point of this equation, the frobenius method allows you to assume that y = Σanxn + r. Then I can take the first and second derivative of this assumption and plug it into the DE and begin solving with the general method: Multiply the...
  23. S

    Frobenius method for Hermite Equation

    Homework Statement I'm asked to solve the Hermite Differential Equation y''(x) - 2 x y'(x) + \lambda y(x) = 0 using the Frobenius method 2. Homework Equations I am to assume the solution is in the form y(x) = \sum a_n x^{n+r} where r are the roots of the indicial equation that in this...
  24. P

    Frobenius method and Euler equations

    Hi, I'm having trouble with this one. Homework Statement Find a particular solution of the second-order homogeneous lineal differential equation x^2y'' + xy' - y = 0 taking in account that x = 0 is a regular singular point and performing a power series expansion. Homework...
  25. A

    Frobenius Method: Solving for General Solution of 4xy'' + 2y' + y = 0 [x7/2]

    ∑Homework Statement Use the method of Frobenius, constructing a power series about x = 0, to find the general solution of this equation (retain terms up to and including those in square brackets): 4xy'' + 2y' + y = 0 [x7/2] Note: the solution can be written in closed form, can you...
  26. C

    MHB How do you find frobenius canonical form of a matrix?

    the actual problem is to show that the given matrix is similar to companion matrix here is the companion matrix Companion matrix - Wikipedia, the free encyclopedia ---------------- i know that if same frobenius canonical form then similar but i don't even know how to find the frobenius...
  27. E

    Frobenius method for fourth order linear ODE

    By using frobenius method I find the roots of the indicial equation of a 4th order ODE to be 0, 1, 1, 2 Now, what is the form of the corresponding series solution of this equation with log terms?
  28. TheFerruccio

    Solve Equation with Method of Frobenius

    Homework Statement Use method of Frobenius to solve this equation: ##y''(x)-y'(x)=x## Homework Equations ------ The Attempt at a Solution Seek an answer of the form ##y=\sum _{n=0}^{\infty } a_n x^{n+r}## Plug into the equation to get... ##\sum _{n=0}^{\infty } a_{n+1} (n+r)...
  29. D

    How do I find the second solution using the Frobenius method?

    Homework Statement I want to find two linearly independent solutions of $$ x^{2}y''-2x^{2}y'+(4x-2)y=0. $$ The Attempt at a Solution The roots to the indicial polynomial are ##r_{1}=2## and ##r_{2}=-1##. I found one solution which was ##x^{2}## and I am having trouble finding the...
  30. U

    Frobenius series without recurrence relation

    Homework Statement Consider x^2y''-xy'+n^2y=0 where n is a constant. a) find two linearly independent solutions in the form of a Frobenius series, initially keeping at least the first 3 terms. Can you find the solution to all orders? b) for n=1 you shouild find only one linearly...
  31. C

    Solve Using Frobenius Method

    Homework Statement Solve x(1-x)\frac{d^{2}y}{dx^{2}}-2\frac{dy}{dx}+2y=0 using the Frobenius Method. Homework Equations R(x)\frac{d^{2}y}{dx^{2}}+\frac{1}{x}P(x)\frac{dy}{dx}+\frac{1}{x^{2}}V(x)y=0 R_{0}s(s-1)+P_{0}s+V_{0}=0 y=\sum^{∞}_{m=0}a_{m}x^{m+s}...
  32. F

    Solve Legendre Polynomial using Method of Frobenius

    Not sure how this can be done. can anyone help?
  33. I

    Proving the Frobenius Norm Identity for Matrices: A Step-by-Step Guide

    Homework Statement Prove ∥A∥F =√trace(ATA), for all A ∈ R m×n Where T= transpose Homework Equations The Attempt at a Solution I tried and i just can prove it by using numerical method. Is there anyway to prove the equation in a correct way?
  34. T

    Solving the O.D.E using Frobenius Method about x=1

    Homework Statement The task is to find an analytic solution to the O.D.E 4(1-x^2)y''-y=0 \hspace{20mm} y'(1)=1 by using an appropriate series solution about x=1. The Attempt at a Solution The singularity at x=1 is regular, which makes me think the Frobenius method is what's meant by...
  35. WannabeNewton

    Proof of Frobenius' Theorem: Directly Showing ##\omega \wedge d\omega = 0##

    Hi guys. Most of my texts have the standard proof of Frobenius' theorem (both the vector field and differential forms versions) and through multiple indirect equivalences conclude that ##\omega \wedge d\omega = 0## implies (locally) that ##\omega = \alpha d\beta## where ##\omega## is a 1-form...
  36. lonewolf219

    Does limit exist as x approaches zero? Frobenius Method DEQ

    Homework Statement what is the limit of (4x^2-1)/(4x^2) when x→0 Homework Equations In order to find the Indicial Equation, do I need to take the limit of p(x) and q(x), the non-constant coefficients? If so, can the limit of this function be found using LH Rule? The Attempt at a...
  37. T

    MATLAB help, code for Frobenius norm

    Hello, I am trying to write a mtlab code to compute Frobenius norm of an mxn matrix A. defined by ||A||_{F} = \sqrt{ \sum_{i=1}^m \sum_{j=1}^n a^{2}_{i,j}} I have so far written this code, but it does not work, if anyone can help /guide me to the right path, would be greatly...
  38. X

    Frobenius method for a differential equations

    Homework Statement The function satisfies the differential equation f''(x) = xf(x) and has boundary conditions f(0) = 1 and f'(0) = 1 Use Frobenius method to solve for f(x) with a taylor expansion of f(x) up to the quartic term a4x4 Homework Equations f(x) = a0 + a1x + a2x2 + a3x3 + a4x4...
  39. U

    MHB How Can the Frobenius Method Be Used to Solve Complex ODEs?

    Ok here's a funny ODE to solve: xy'' + (1-2x)y' + (x-1)y = 0 clearly a straight forward power series substitution won't work here since we have a regular singularity at x = 0 so try the frobenius method by expanding around x = 0. Assume y = \sum_{m=0}^{\infty} a_mx^{m+r} is a solution where...
  40. S

    MHB Solving DE using Frobenius series method

    Solve xy'= y using frobenius method The explanation given in the book is very confusing can somebody explain in simple method. Thanks
  41. V

    Differential eqations and frobenius method

    Homework Statement y''+4xy'+(4x^2+2)y=0 find the basis of solutions using the frobenius method. can anyone solve this please...
  42. T

    Proving the Frobenius Norm as a Matrix Norm

    Homework Statement Prove that the Frobenius norm is indeed a matrix norm. Homework Equations The definition of the the Frobenius norm is as follows: ||A||_F = sqrt{Ʃ(i=1..m)Ʃ(j=1..n)|A_ij|^2} The Attempt at a Solution I know that in order to prove that the Frobenius norm is indeed...
  43. S

    Using Frobenius theorem

    Homework Statement In Problems 25–30, x=0 is a regular singular point of the given differential equation. Show that the indicial roots of the singularity differ by an integer. Use the method of Frobenius to obtain at least one series solution about x=0...
  44. A

    Frobenius Method - Roots differ by integer

    I'm reading up on some methods to solve differential equations. My textbook states the following: "y_{1} and y_{2} are linearly independent ... since \sigma_{1}-\sigma_2 is not an integer." Where y_{1} and y_{2} are the standard Frobenius series and \sigma_1 and \sigma_2 are the roots of...
  45. C

    Solving Schrodinger DE using Frobenius

    My DE is \frac{h^2}{2m} \frac{d^2\psi}{dx^2} + \left(E - \frac{Ae^{-ax}}{x} \right) \psi = 0 where h, m, A < 0 and a and E are constants. I need to construct the following series solution (using the larger root of my indicial equation): \psi(x) = a_0 \left[x + \frac{Am}{h^2}x^2 +...
  46. G

    When is the Frobenius norm of a matrix equal to the 2-norm of a matrix?

    What conditions most be true for these two norms to be equal? Or are they always equal?
  47. S

    Theoretical/non-tedious question about Frobenius method

    When using the Frobenius method of solving differential equations using power series solutions, I get a solution y = (indicial_stuff) + (infinite_summation_stuff) = 0 for a differential equation differential_stuff = 0. WHY is it that I can say (indicial_stuff) = 0? If y =...
  48. R

    Variations of the Frobenius coin problem

    I wasn't sure if this should go in the number theory section, but here goes: Is there a formula for solving problems such as: If there are n coin denominations x_{1},x_{2}...x_{n} that total p cents, how many combinations are possible? n and p are positive real numbers, of course. On a...
  49. Telemachus

    Second order diff. eq. Frobenius

    Hi there. I have this exercise, which says: Demonstrate that: xy''+(1-x)y'+\lambda y=0 has a polynomial solution for some λ values. Indicate the orthogonality relation between polynomials, the fundamental interval, and the weight function. So I thought I should solve this using Frobenius...