Optimizing Work: Finding the Minimum Path in Non-Conservative Vector Fields

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Discussion Overview

The discussion centers on finding the path that requires the least amount of work in non-conservative vector fields, exploring both theoretical and numerical methods for optimization. Participants consider various approaches to minimize work from point A to point B, including the use of the Calculus of Variations and ordinary differential equations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant inquires about methods to find the least work path in non-conservative vector fields and asks for numerical approximation techniques.
  • Another participant suggests using the Calculus of Variations, proposing the determination of a Lagrangian and solving the Euler Lagrange equations.
  • A follow-up question seeks clarification on what specific Lagrangian should be set up for this problem.
  • One participant proposes taking the Lagrangian as "1" to minimize path length.
  • Another participant describes a method involving solving a system of ordinary differential equations derived from the vector field, emphasizing the importance of step size in numerical solutions.
  • A later reply connects the least energy path to the minimum action principle and Newton's Second Law, suggesting that the path followed by a particle will satisfy the corresponding ordinary differential equation.

Areas of Agreement / Disagreement

Participants present multiple approaches and methods to tackle the problem, indicating that there is no consensus on a single solution or method. Various techniques are proposed, and the discussion remains open-ended regarding the best approach.

Contextual Notes

Participants express uncertainty about the specific setup of the Lagrangian and the implications of different methods. There are unresolved aspects regarding the numerical approximation techniques and the conditions under which the proposed methods would be effective.

goffinj
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I was wondering, if you have a non-conservative vector field (so that the line integral of each path from point A to point B isn't the same) that represents some sort of force, then is there a method to find the path that requires the least amount of work from a designated point A to point B? Even if you can't calculate it exactly is there a numerical approximation for such a path? Thanks for any help or suggestions.
 
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The technique you would use to solve this kind of problem is the Calculus of Variations. You just need to determine a Lagrangian and then solve the Euler Lagrange equations.
 
What Lagrangian would you set up?

We want to find the path that minimizes W = integral F dot dr. How do you solve for a path?

I apologize for the sloppy notation; this is my first post and I'm not familiar with tricks to get the integral and dot product signs to show up.
 
Just take your "Lagrangian" to be "1". That way minimizing the value will minimize the path length.
 
There's an absurdly simple way to solve this problem.

For position x, vector field v is given by v(x). Solve

dx/dt = v(x)

where t is a parameter: x = x(t).

It's a system of ordinary differential equations, but such equations should be easy to solve numerically. The main problem is keeping the ODE-solver step size in a reasonable range.
 
The path that takes the least energy, is the path that an actual particle will travel along (a result of minimum action principle) which is the path that abides Newton's Second Law, so it will solve the ODE:

\frac{d^{2}\vec{x}}{dt^{2}}=\vec{F}(\vec{x})

(F being the vector field)
 

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