Lagrange Definition and 541 Threads

Joseph-Louis Lagrange (born Giuseppe Luigi Lagrangia or Giuseppe Ludovico De la Grange Tournier; 25 January 1736 – 10 April 1813), also reported as Giuseppe Luigi Lagrange or Lagrangia, was an Italian mathematician and astronomer, later naturalized French. He made significant contributions to the fields of analysis, number theory, and both classical and celestial mechanics.
In 1766, on the recommendation of Swiss Leonhard Euler and French d'Alembert, Lagrange succeeded Euler as the director of mathematics at the Prussian Academy of Sciences in Berlin, Prussia, where he stayed for over twenty years, producing volumes of work and winning several prizes of the French Academy of Sciences. Lagrange's treatise on analytical mechanics (Mécanique analytique, 4. ed., 2 vols. Paris: Gauthier-Villars et fils, 1788–89), written in Berlin and first published in 1788, offered the most comprehensive treatment of classical mechanics since Newton and formed a basis for the development of mathematical physics in the nineteenth century.
In 1787, at age 51, he moved from Berlin to Paris and became a member of the French Academy of Sciences. He remained in France until the end of his life. He was instrumental in the decimalisation in Revolutionary France, became the first professor of analysis at the École Polytechnique upon its opening in 1794, was a founding member of the Bureau des Longitudes, and became Senator in 1799.

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  1. F

    Horizontal Circular Motion With Lagrange

    In the situation described in the problem, the mass is moving on a horizontal circular path with constant velocity. Wouldn’t this make L and U both constant? Then the Lagrange equation would give 0 = 0, which isn’t what I’m looking for. Any help would be appreciated.
  2. W

    Lagrange Equations of Motion for a particle in a vessel

    The final answer should have a negative b^2⋅r(dot)^2⋅r term but I have no idea how that term would become negative. Also I know for a fact that my Lagrangian is correct.
  3. W

    Lagrange Equations of Motion for a particle in a vessel

    I start out by substituting rcos(Θ) and rsin(Θ) for x and y respectively. This gives me z=(b/2)r^2. The Lagrangian of this system is (1/2)m(rdot^2+r^2⋅Θdot^2+zdot^2)-mgz. (rdot and such is the time derivative of said variable). I then find the time derivative of z, giving me zdot=br⋅rdot and...
  4. dRic2

    Finding the minimum of an integral with Lagrange multipliers

    Using Lagrange multiplier ##\lambda## (only one is needed) the integral to minimize becomes $$\int_{\tau_1}^{\tau_2} (y + \lambda) \sqrt{{x'}^2+{y'}^2} d \tau = \int_{\tau_1}^{\tau_2} F(x, x', y, y', \lambda, \tau) d\tau $$ Using E-L equations: $$\frac {\partial F}{\partial x} - \frac d {d \tau}...
  5. PhillipLammsoose

    I Problem with the harmonic oscillator equation for small oscillations

    Hey, I solved a problem about a double pendulum and got 2 euler-lagrange equations: 1) x''+y''+g/r*x=0 2) x''+y'' +g/r*y=0 (where x is actually a tetha and y=phi) the '' stand for the 2nd derivation after t, so you can see the basic harmonic oscillator equation with a term x'' or y'' that...
  6. J

    I How can an asteroid get caught at a Lagrange point without a "brake"?

    Talking about the Jupiter Lagrange points at 60 degrees only. Hard to imagine a scenario where an asteroid comes from outside or inside the orbit of Jupiter and stops at a Lagrange point. That's like tossing a cone on a table and trying to make it end up standing on its nose. Or make the nose...
  7. S

    Lagrange error bound inequality for Taylor series of arctan(x)

    The error ##e_{n}(y)## for ##\frac{1}{1-y}## is given by ##\frac{1}{(1-c)^{n+2}}y^{n+1}##. It follows that ##\frac{1}{1+y^2}=t_n(-y^2)+e_n(-y^2)## where ##t_n(y)## is the Taylor polynomial of ##\frac{1}{1-y}##. Taking the definite integral from 0 to ##x## on both sides yields that...
  8. M

    How to Derive Equations of Motion from Lagrange Density?

    Homework Statement I'd like to derive the equations of motion for a system with Lagrange density $$\mathcal{L}= \frac{1}{2}\partial_\mu\phi\partial^\mu\phi,$$ for ##\phi:\mathcal{M}\to \mathbb{R}## a real scalar field. Homework Equations $$\frac{\partial...
  9. F

    Writing: Input Wanted Duration: flights to L-4 point, and 90 degrees Earth orbit

    Assumptions: 200+ years from now Asteroids have been moved to all Lagrange points, and at least 90, 180, and 270 degrees on Earth's' orbit for mining, and shielding humans and equipment Tech to acceleration/decelerate at 1 gravity without need to carry fuel. (My main fiction.) Direct line of...
  10. H

    A Lagrange Densities: Intuitive Understanding

    I'm a little confused when we transition from the Lagrangian of a point particle to consider Lagrangian of objects with dimension bigger then zero. For instance, the Lagrangian of a string is the sum of the Lagrangians for each infinitesimal part of the object. which means we are integrating...
  11. A

    I How to derive Nielsen equation from Lagrange equation?

    How to derive Nielsen equation from Lagrange equation
  12. L

    Lagrange equation of second kind - find solution's constant?

    Homework Statement This could be a more general question about pendulums but I'll show it on an example. We have a small body (mass m) hanging from a pendulum of length l. The point where pendulum is hanged moves like this: \xi = A\sin\Omega t, where A, \Omega = const. We have to find motion...
  13. H

    B Feasibility of a L1 Gravity Swing Cold Launch?

    At an L1 LaGrangian point between two bodies, one could - materials science notwithstanding - pit two of Newton's Laws (LM3,UG) against each other to provide thruster-free stationkeeping. Would it be feasible to use that to launch free from the system ? either spit out like a watermelon seed...
  14. Rabindranath

    A Lagrange multipliers on Banach spaces (in Dirac notation)

    I want to prove Cauchy–Schwarz' inequality, in Dirac notation, ##\left<\psi\middle|\psi\right> \left<\phi\middle|\phi\right> \geq \left|\left<\psi\middle|\phi\right>\right|^2##, using the Lagrange multiplier method, minimizing ##\left|\left<\psi\middle|\phi\right>\right|^2## subject to the...
  15. benorin

    Lagrange Multipliers inconsistent system

    Homework Statement maximize f(a,d,h,p)= (4a+3d+3h+c1)c2 *(2+0.01*floor(50+0.0001p)) subject to the constraint 1439a+427d+9259+912/5*h=k. This is not a homework problem but it may as well be: it comes from a game, the function f represents damage as a function of 4 stats and the constraint...
  16. R

    Lagrange multipliers: help solving for x, y and lambda

    Homework Statement Find the local extreme values of ƒ(x, y) = x2y on the line x + y = 3 Homework Equations ∇ƒ = λ∇g The Attempt at a Solution 2yxi+x^2j = λi + λj [2yx=λ] [x^2=λ] [x+y=3] [2yx=x^2] & [(2y)+y=3] [2y=x] & [y=1]...
  17. Phylosopher

    Conservation laws from Lagrange's equation

    My question is related to the book: Classical Mechanics by Taylor. Section 7.8 So, In the book Taylor is trying to derive the conservation of momentum and energy from Lagrange's equation. I understood everything, but I am struggling with the concept and the following equation...
  18. sams

    A Partial Differentiation in Lagrange's Equations

    In Section 7.6 - Equivalence of Lagrange's and Newton's Equations in the Classical Dynamics of Particles and Systems book by Thornton and Marion, pages 255 and 256, introduces the following transformation from the xi-coordinates to the generalized coordinates qj in Equation (7.99): My...
  19. B

    Lagrange and cubic spline interpolate

    Homework Statement This is a bit unusual, I don't know whether I should post it here or math forum tbh. When I was doing numerical method home work, I am required to do perform both of these interpolation on a set of 4 data points. It turns out that the result of these 2 methods always agrees...
  20. T

    I Minimization using Lagrange multipliers

    Given the following expressions: and that ## \bf{B}_s = \nabla \times \bf{A}_s ## how does one solve for the following expressions given in (12) and (13)? I've attempted doing so and derive the following expressions (where the hat indicates a unit vector): ## bV = \bf{ \hat{V}} \cdot...
  21. petterson

    A Maximization problem using Euler Lagrange

    Hi, I'm trying to solve the following problem ##\max_{f(x)} \int_{f^{-1}(0)}^0 (kx- \int_0^x f(u)du) f'(x) dx##. I have only little experience with calculus of variations - the problem resembles something like ## I(x) = \int_0^1 F(t, x(t), x'(t),x''(t))dt## but I don't know about the...
  22. S

    I Euler Lagrange formula with higher derivatives

    I was trying to Extrapolate Eulers formula , after deriing the basic form I wanted to prove: ∂F/∂y - d(∂F/∂yx)/dx +d[SUP]2[/SUP](∂F/∂yxx)/dx2 = 0 Here is my attempt but I get different answers: J(y) = ∫abF(x,yx,y,yxx)dx δ(ε) = J(y+εη(x)) y = yt+εη(x) ∂y/∂ε = η(x) ∂yx/∂ε = η⋅(x)...
  23. L

    A How many cosets are there when taking a subgroup in a group and forming cosets?

    When we take some subgroup ##H## in ##G##. And form cosets ##g_1H, g_2H,...,g_{n}H##. Is ##H## also coset ##eH##, where ##e## is neutral? So do we have here ##n## or ##n+1## cosets?
  24. jamalkoiyess

    I Delta x in the derivation of Lagrange equation

    Hello PF, I was doing the derivation of the Lagrange equation of motion and had to do some calculus of variations. The first step in the derivation is to multiply the integral of ƒ(y(x),y'(x);x)dx from x1 to x2 by δ. and then by the chain rule we proceed. But I cannot understand why we are...
  25. W

    Comparing Generalised Momentum Calculations for Central Force Problems

    Homework Statement I have an issue with understanding the idea of generalised momentum for the Lagrangian. For a central force problem, the Lagrangian is given by, $$L = \frac{1}{2}m(\dot{r} ^2 + p^2 \dot{\phi ^2}) - U(r)$$ with ##r## being radial distance. The angular momentum is then...
  26. mcaay

    Lagrange Multipliers in Classical Mechanics - exercise 1

    Homework Statement The skier is skiing without friction down the mountain, being all the time in a specified plane. The skier's altitude y(x) is described as a certain defined function of parameter x, which stands for the horizontal distance of the skier from the initial position. The skier is...
  27. V

    I Values of Lagrange multipliers when adding new constraints

    Say we have a Lagrange function with one multiplier a times a constrain. I minimize and solve the system to find a. I now add another constrain to the same system multiplied by the constant b. Is the value of a the same or can it change?
  28. C

    A Derivation of Euler Lagrange, variations

    What is wrong with the simple localised geometric derivation of the Euler Lagrange equation. As opposed to the standard derivation that Lagrange provided. Sorry I haven't mastered writing mathematically using latex. I will have a look at this over the next few days. More clarification. I...
  29. M

    I Optimizing fractions and Lagrange Multiplier

    Hi PF! When minimizing some fraction ##f(x)/g(x)## can we use Lagrange multipliers and say we are trying to optimize ##f## subject to the constraint ##g=1##? Thanks
  30. Dr Wu

    B Earth-Sun Lagrange Points Distance Query

    Hi Does anyone know what the straight line distances of L4 and L5 are from Earth? Many thanks.
  31. Andrew Deleonardis

    I Lagrange Pendulum Equation of Motion

    Hi, I've derived the equation of motion for a regular single pendulum, but do not know how to solve the differential equation. I have the following: r2θ''2=mg(cosθ-rsinθ)
  32. zwierz

    A The Lagrange Top: Formulas and Analysis for Non-Zero Angular Momentum Cases

    All the needed formulas are here http://hepweb.ucsd.edu/ph110b/110b_notes/node36.html I consider the following case $$p_\psi\ne 0,\quad p_\phi/p_\psi\in (\cos\theta_2,\cos\theta_1)$$ this case corresponds to the middle picture in the bottom of the cited page. I can not prove that the time...
  33. P

    Is the Lagrange Equation Valid for All Holonomic Systems?

    Homework Statement Show that for an arbitrary ideal holonomic system (n degrees of freedom) \frac{1}{2} \frac{\partial \ddot T}{\partial\ddot q_j} - \frac{3}{2} \frac{\partial T}{\partial q_j} = Q_j where T is kinetic energy and qj generalized coordinates.[/B]Homework Equations...
  34. harpazo

    MHB What are the steps for solving a problem using Lagrange Multipliers?

    Use Lagrange Multipliers to find the individual extrema, assuming that x and y are positive. Maximize: f (x, y) = e^(xy) Constraint: x^2 + y^2 = 8 My Work: I decided to rewrite the constraint as x^2 + y^2 without the constant 8 as originally given. g (x, y) = x^2 + y^2 I found the gradient...
  35. harpazo

    MHB Finding Extrema with Lagrange Multipliers

    Use Lagrange Multipliers to find the individual extrema, assuming that x and y are positive. Maximize: f (x, y) = sqrt {6 - x^2 - y^2} Constraint: x + y - 2 = 0 My Work: I first decided to rewrite the constraint as g (x, y) = x + y without the constant -2 as originally given. I found the...
  36. nomadreid

    I Why are Lagrange points called libration points, and....

    Two questions about Lagrange points. (1) According to Wikipedia, "libration is a perceived oscillating motion of orbiting bodies relative to each other," whereas the Lagrange points are, with respect to two bodies, null points for a (real or hypothetical) third body with respect to the sum...
  37. Kaura

    Unbounded Feasible Region for Lagrange with Two Constraints

    Homework Statement Homework Equations Partials for main equation equal the respective partials of the constraints with their multipliers The Attempt at a Solution Basically I am checking to see if this is correct I am pretty sure that 25/3 is the minimum but I am not sure how to find...
  38. F

    Euler Lagrange equation issue with answers final form

    Homework Statement For the following integral, find F and its partial derivatives and plug them into the Euler Lagrange equation $$F(y,x,x')=y\sqrt{1+x'^2}\\$$ Homework Equations Euler Lagrange equation : $$\frac{dF}{dx}-\frac{d}{dy}\frac{dF}{dx'}=0$$ The Attempt at a Solution...
  39. A

    Expressing a quadratic form in canonical form using Lagrange

    Problem: Express the quadratic form: q=x1x2+x1x3+x2x3 in canonical form using Lagrange's Method/Algorithm Attempt: Not really applicable in this case due to the nature of my question The answer is as follows: Using the change of variables: x1=y1+y2 x2=y1-y2 x3=y3 Indeed you get...
  40. K

    I Solve Lagrange Multiplier Mystery: ∂Σ{Ni}/∂Nj = ∂N/∂Nj=0

    Hi, I have a question about lagrange multiplier Let's say we are given with the following constraints Σ{Ni}=N and Σ{NiEi}=total energy. N and total energy are constants by definition. if we take the derivative with respect to Nj, ∂Σ{Ni}/∂Nj=∂N/∂Nj where i=j, ∂Σ{Ni}/∂Nj=1 and ∂N/∂Nj = 0...
  41. N

    Maximum of entropy and Lagrange multiplier

    Hello, I have to find the density of probability which gives the maximum of the entropy with the following constraint\bar{x} = \int x\rho(x)dx \int \rho(x) dx = 1 the entropy is : S = -\int \rho(x) ln(\rho(x)) dx L = -\int \rho(x) ln(\rho(x)) dx - \lambda_1 ( \int \rho(x) dx -1 ) -...
  42. S

    I Deriving Lagrange's Equation: Help Understanding Chain Rule

    am deriving lagrange's equation can anybody help me to understand this identity the book says that he is using the chain rule for it but am not getting it d/dt(∂x/∂q) the identity is in the screen shot thanks :)
  43. M

    Minimizing weight of a cylinder using Lagrange multipliers

    Homework Statement Julia plans to make a cylindrical vase in which the bottom of the vase is 0.3 cm thick and the curved, lateral part of the vase is to be 0.2 cm thick. If the vase needs to have a volume of 1 liter, what should its dimensions be to minimize its weight? Homework Equations...
  44. King_Silver

    I Lagrange Multiplier. Dealing with f(x,y) =xy^2

    Given a question like this: Findhe maximum and minimum of http://tutorial.math.lamar.edu/Classes/CalcIII/LagrangeMultipliers_files/eq0043M.gif[PLAIN]http://tutorial.math.lamar.edu/Classes/CalcIII/LagrangeMultipliers_files/empty.gif subject to the constraint...
  45. Gopal Mailpalli

    Classical Good book for Lagrangian and Hamiltonian Mechanics

    This book should introduce me to Lagrangian and Hamiltonian Mechanics and slowly teach me how to do problems. I know about Goldstein's Classical Mechanics, but don't know how do I approach the book.
  46. DuckAmuck

    A Shape of a pinned canvas w/ Lagrange Multipliers

    I'm basically trying to understand the 2-D case of the catenary cable problem. The 1-D case is pretty straightforward, you have a functional of the shape of a cable with a constraint for length and gravity, and you get the explicit function of the shape of a cable. But if you imagine a square...
  47. M

    Deriving the thermodynamic beta from Lagrange Multipliers

    I'm nearly at the end of this derivation but totally stuck so I'd appreciate a nudge in the right direction Consider a set of N identical but distinguishable particles in a system of energy E. These particles are to be placed in energy levels ##E_i## for ##i = 1, 2 .. r##. Assume that we have...
  48. mr.tea

    I Lagrange multipliers and critical points

    Hi, I have (probably) a fundamental problem understanding something related critical points and Lagrange multipliers. As we know, if a function assumes an extreme value in an interior point of some open set, then the gradient of the function is 0. Now, when dealing with constraint...
  49. Samia qureshi

    What is the Lagrange Multiplier

    Can anybody explain in simple and easy words "Lagrange Multiplier" What is it? and when it is used? i googled it but that was explained in much difficult words.
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