Numerical Solution for Complex PDE (Ginzburg-Landau Eqn.)

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Discussion Overview

The discussion revolves around numerically solving the complex Time Domain Ginzburg-Landau Equation (TDGL) using Python. Participants explore methods for implementing a fourth order Runge-Kutta (RK4) algorithm for complex variables, the handling of Laplacians in complex fields, and the challenges of simulating fluxon nucleation in superconductors.

Discussion Character

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

Main Points Raised

  • One participant seeks guidance on implementing the RK4 algorithm for complex variables, noting that existing solvers do not handle complex numbers well.
  • Another participant suggests that the RK4 method can be applied separately to the real and imaginary parts of the complex variable.
  • There is a discussion about the necessity of modifying the RK implementation despite Python's capability to handle complex numbers, with one participant questioning the need for separation of real and complex parts.
  • Participants propose simple test cases for validating the RK4 implementation, including equations with known solutions.
  • One participant inquires about implementing a complex Laplacian, expressing uncertainty about whether the same convolutional kernel used for real values can be applied to complex values.
  • Another participant mentions the difficulty of handling the nonlinear term in the PDE and suggests exploring finite element methods or trial functions for correction.
  • One participant shares their simulation results, noting that their implementation aligns closely with a referenced paper, but expresses confusion about the computation of the nonlinear term.
  • There is a suggestion to consider system size and the potential use of exponential time integration schemes in Fourier space.
  • Participants discuss the behavior of fluxon cores in the simulation, noting issues such as cores not moving and potential overflow problems in the computation.

Areas of Agreement / Disagreement

Participants express various viewpoints on the implementation of numerical methods, the handling of complex variables, and the challenges posed by the nonlinear terms in the TDGL equation. There is no consensus on the best approach or method to resolve the issues raised.

Contextual Notes

Participants highlight limitations in their current methods, such as the handling of the nonlinear term and the potential for overflow in simulations. There are also references to specific mathematical techniques and numerical methods that may not be universally applicable.

Who May Find This Useful

Researchers and practitioners interested in numerical methods for solving complex partial differential equations, particularly in the context of superconductivity and related fields.

  • #31
Twigg said:
Finite difference is the method I was thinking of. Specifically, a central-difference scheme for the Laplacian. The catch is that your problem is non-linear due to the |ψ|2ψ|\psi|^{2} \psi term. You will need to use Newton's method to get a solution, and that opens a new can of worms with convergence and validation. I've never tried this personally, but I know at least one piece of commercial software (COMSOL) that uses Newton's method to solve the matrix problems of finite element methods.

Why would you think there is a problem with non-linear terms? I really can not see how this should pose a problem as long as he uses some explicit time integration scheme ( and even if he used an implicit I can not see why the difficulties would even be related to the finite difference method ).
 
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  • #32
Strum said:
Why would you think there is a problem with non-linear terms? I really can not see how this should pose a problem as long as he uses some explicit time integration scheme ( and even if he used an implicit I can not see why the difficulties would even be related to the finite difference method ).
You're absolutely right, my mistake. I was thinking of a steady-state problem, which this is not.
 

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