Euler-Lagrange Equations with constraint depend on 2nd derivative?

In summary, Neuenschwander's book discusses Noether's Theorem and the Euler-Lagrange equations. The equations can be derived from the integral of a Lagrangian and can also incorporate constraints of the form h(t,x^\mu)=0. This constraint does not depend on \dot x^\mu, and if it did, it would invalidate the Euler-Lagrange equations. Constraints on the \dot x^\mu can be introduced with a rheonomic constraint, which is explicitly time dependent.
  • #1
birulami
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I am reading the book of Neuenschwander about Noether's Theorem. He explains the Euler-Lagrange equations by starting with

[tex]J=\int_a^b L(t,x^\mu,\dot x^\mu) dt[/tex]

From this he derives the Euler-Lagrange equations

[tex]\frac{\partial L}{\partial x^\mu} = \frac{d}{dt}\frac{\partial L}{\partial \dot x^\mu}[/tex]

which is all well comprehensible. Then he describes how to introduce constraints of the form [itex]h(t,x^\mu)=0[/itex] to form a lagrangian with constraint [itex]L_c = L+\lambda h[/itex].

My question: The constraint does not depend on [itex]\dot x^\mu[/itex]. Is this just to simplify the derivation in this case or would a constraint [tex]h(t,\dot x^\mu)=0[/tex] invalidate the Euler-Lagrange equations? If the latter is true, how would we introduce constraints on the [itex]\dot x^\mu[/itex]?
 
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  • #2
This is called a holonomic constraint (but it's rheonomic because it's explicitly time dependent). A constraint is anholonomic if it's a non-integrable equation of both the generalized coordinates and velocities.
 

1. What are Euler-Lagrange equations?

The Euler-Lagrange equations are a set of equations used to find the extrema of a functional. They are derived from the calculus of variations and are used in various fields such as physics and engineering to solve optimization problems.

2. How do constraint depend on 2nd derivative impact Euler-Lagrange equations?

When constraints depend on the 2nd derivative, the Euler-Lagrange equations become more complex. In these cases, the constraints are typically incorporated into the equations using the method of undetermined multipliers, resulting in a set of modified Euler-Lagrange equations.

3. What is the significance of the 2nd derivative in Euler-Lagrange equations?

The 2nd derivative plays a crucial role in the Euler-Lagrange equations as it represents the rate of change of the first derivative. It allows for more complex constraints to be incorporated into the equations, making them more versatile in solving optimization problems.

4. How are Euler-Lagrange equations with constraint depend on 2nd derivative solved?

Euler-Lagrange equations with constraint depend on 2nd derivative can be solved using the method of undetermined multipliers. This involves introducing additional variables, known as Lagrange multipliers, to incorporate the constraints into the equations. The resulting system of equations can then be solved using standard methods.

5. What are some real-world applications of Euler-Lagrange equations with constraint depend on 2nd derivative?

Euler-Lagrange equations with constraint depend on 2nd derivative have various applications in fields such as mechanics, economics, and control theory. They can be used to solve problems related to optimal control, optimal design, and stability analysis, among others.

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