Relaxed Lagrange Multiplier (RLM) Schemes for Phase Field Models Preserving the Relaxed Original Energy Dissipation Law
Pith reviewed 2026-07-02 00:21 UTC · model grok-4.3
The pith
Relaxed Lagrange multiplier schemes dissipate a relaxed version of the original energy in phase field models while remaining uniquely solvable over broad time steps.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The RLM schemes dissipate a relaxed version of the original energy, closely track the original energy dissipation rate, and ensure the resulting discrete system is uniquely solvable over a broad range of time steps. The key step is augmenting the classical Lagrange multiplier formulation with a relaxation term that produces a scalar quadratic equation for the multiplier with an explicit closed-form solution.
What carries the argument
The relaxation term added to the Lagrange multiplier formulation, which produces an explicit closed-form solution for the multiplier via a scalar quadratic equation while preserving energy stability.
If this is right
- The schemes remain linear and require solving only two linear systems with constant coefficients per time step.
- Both first-order and second-order variants satisfy the energy stability property.
- Numerical tests confirm the expected convergence orders and accurate reproduction of interface dynamics.
- Computational cost per step matches that of scalar auxiliary variable schemes.
Where Pith is reading between the lines
- The same relaxation idea could extend to multiplier-based discretizations of other variational evolution equations.
- Wider stable time-step ranges could allow longer simulations of multiphase systems without loss of stability.
- Closer adherence to the original dissipation law may reduce artifacts in applications where auxiliary variables change the underlying dynamics.
Load-bearing premise
Augmenting the Lagrange multiplier formulation with a relaxation term produces a scalar quadratic equation that admits an explicit closed-form solution while preserving energy stability and the ability to track the original dissipation law.
What would settle it
A numerical test on a standard phase field model in which the algebraic system at a time step has no real solution or multiple solutions, or the computed energy fails to follow the claimed relaxed dissipation law.
Figures
read the original abstract
Phase-field models are typically derived from variational principles for a free-energy functional and are widely used to simulate complex multiphase phenomena in science and engineering. A central goal in designing numerical schemes for these models is to preserve the underlying energy-dissipation law. In this paper, we propose a class of relaxed Lagrange multiplier (RLM) schemes for phase field models. In contrast to popular scalar auxiliary variable (SAV) and invariant energy quadratization (IEQ) methods, which dissipate a modified energy involving auxiliary variables, the RLM schemes dissipate a relaxed version of the original energy and closely track the original energy dissipation rate. Compared with the classical Lagrange multiplier (LM) approach, the RLM schemes ensure that the resulting discrete system is uniquely solvable over a broad range of time steps. The key idea is to augment the LM formulation with a relaxation term, yielding a scalar quadratic equation for the multiplier with an explicit closed-form solution. The resulting schemes are linear and efficient because each time step requires solving only two linear systems with constant coefficients, at a cost comparable to that of SAV schemes. We construct both first-order and second-order variants and prove their energy stability. Numerical experiments verify the expected convergence rates and demonstrate that the RLM schemes accurately capture interface dynamics.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript proposes relaxed Lagrange multiplier (RLM) schemes for phase field models. Unlike SAV and IEQ methods that dissipate modified energies, the RLM schemes dissipate a relaxed version of the original energy while closely tracking the original dissipation rate. The key construction augments the classical LM formulation with a relaxation term to produce a scalar quadratic equation for the multiplier that admits an explicit closed-form solution, ensuring the discrete system is uniquely solvable over a broad range of time steps. The resulting schemes are linear, requiring only two linear solves with constant coefficients per step at a cost comparable to SAV. Both first- and second-order variants are constructed and proved energy stable; numerical experiments are reported to confirm convergence rates and accurate capture of interface dynamics.
Significance. If the stated energy-stability proofs and numerical results hold, the contribution would be significant for structure-preserving discretizations of phase-field models. The approach directly addresses two well-known limitations of existing methods: the use of auxiliary energies in SAV/IEQ and the solvability restrictions of classical LM schemes, while retaining linear cost. Explicit closed-form treatment of the multiplier and preservation of a relaxed original energy law would be attractive features for long-time simulations of multiphase phenomena.
major comments (2)
- The abstract asserts that energy stability is proved for the first- and second-order RLM schemes and that the schemes 'closely track the original energy dissipation rate,' yet the provided text contains neither the augmented formulation, the quadratic equation, nor any derivation. Without these details the central claims cannot be verified.
- The claim that the discrete system is 'uniquely solvable over a broad range of time steps' is load-bearing for the practical advantage over classical LM methods, but no range, no explicit solution formula, and no solvability analysis appear in the available material.
Simulated Author's Rebuttal
We thank the referee for their careful summary and for highlighting the central claims of the work. We address the major comments point by point below. Only the abstract is available in the provided manuscript material.
read point-by-point responses
-
Referee: The abstract asserts that energy stability is proved for the first- and second-order RLM schemes and that the schemes 'closely track the original energy dissipation rate,' yet the provided text contains neither the augmented formulation, the quadratic equation, nor any derivation. Without these details the central claims cannot be verified.
Authors: The abstract is a concise summary and does not contain the technical derivations. The augmented formulation, the quadratic equation for the multiplier, and the energy-stability proofs for the first- and second-order schemes are developed in the body of the full manuscript. Because only the abstract is supplied here, those details cannot be reproduced in this response. revision: no
-
Referee: The claim that the discrete system is 'uniquely solvable over a broad range of time steps' is load-bearing for the practical advantage over classical LM methods, but no range, no explicit solution formula, and no solvability analysis appear in the available material.
Authors: The abstract states unique solvability over a broad range of time steps as a distinguishing feature. The explicit closed-form solution, the admissible range of time steps, and the accompanying solvability analysis appear in the full manuscript, which is not included in the provided text. revision: no
- Augmented formulation, quadratic equation, and energy-stability derivations
- Explicit solution formula, admissible time-step range, and solvability analysis
Circularity Check
No significant circularity identified
full rationale
Only the abstract is available, which describes the RLM method as a direct augmentation of the classical LM formulation by adding a relaxation term to produce a solvable quadratic equation while preserving a relaxed energy dissipation law. No equations, proofs, fitted parameters, or self-citations are supplied that could trigger any of the enumerated circularity patterns. The construction is presented as an independent design choice with separately proven stability, making the derivation self-contained against external benchmarks.
Axiom & Free-Parameter Ledger
Reference graph
Works this paper leans on
-
[1]
S. M. Allen. Ground state structures in ordered binary alloys with second neighbor interactions. Acta Metallurgica, 20(3):423–433, 1972
1972
-
[2]
D. M. Anderson, G. B. McFadden, and A. A. Wheeler. Diffuse-interface methods in fluid mechanics.Annual Review of Fluid Mechanics, 30(1):139–165, 1998
1998
-
[3]
J. W. Cahn and J. E. Hilliard. Free energy of a nonuniform system. I. Interfacial free energy. Journal of Chemical Physics, 28(2):258–267, 1958
1958
-
[4]
L. Chen, J. Zhao, and X. Yang. Regularized linear schemes for the molecular beam epitaxy model with slope selection.Applied Numerical Mathematics, 128:138–156, 2018
2018
-
[5]
L. Q. Chen and J. Shen. Applications of semi-implicit Fourier-spectral method to phase field equations.Computer Physics Communications, 108:147–158, 1998
1998
-
[6]
Y. Chen, Z. Liu, and X. Meng. Partially and fully implicit multi-step SAV approaches with original dissipation law for gradient flows.Communications in Nonlinear Science and Numer- ical Simulation, 140:108379, 2025
2025
-
[7]
Cheng, Z
K. Cheng, Z. Qiao, and C. Wang. A third order exponential time differencing numerical scheme for no-slope-selection epitaxial thin film model with energy stability.Journal of Scientific Computing, 81(1):154–185, 2019
2019
-
[8]
Cheng, C
Q. Cheng, C. Liu, and J. Shen. A new Lagrange multiplier approach for gradient flows. Computer Methods in Applied Mechanics and Engineering, 367:113070, 2020
2020
-
[9]
Cheng, J
Q. Cheng, J. Shen, and C. Wang. Unique solvability and error analysis of a scheme using the Lagrange multiplier approach for gradient flows.SIAM Journal on Numerical Analysis, 63(2):772–799, 2025
2025
-
[10]
Numerical analysis of the Cahn-Hilliard equation with a logarithmic free energy.Numerische Mathematik, 63(1):39–65, 1992
Maria Inˆ es Martins Copetti and Charles M Elliott. Numerical analysis of the Cahn-Hilliard equation with a logarithmic free energy.Numerische Mathematik, 63(1):39–65, 1992
1992
-
[11]
C. K. Doan, T. T. P. Hoang, L. Ju, and R. Lan. Dynamically regularized Lagrange multiplier method for the Cahn–Hilliard–Navier–Stokes system.International Journal for Numerical Methods in Engineering, 126(13):e70074, 2025
2025
-
[12]
C. K. Doan, L. Ju, and R. Lan. Dynamically regularized Lagrange multiplier schemes with energy dissipation for the incompressible Navier–Stokes equations.Journal of Computational Physics, 521:113550, 2025
2025
-
[13]
Q. Du, L. Ju, X. Li, and Z. Qiao. Maximum principle preserving exponential time differenc- ing schemes for the nonlocal Allen–Cahn equation.SIAM Journal on Numerical Analysis, 57(2):875–898, 2019
2019
-
[14]
Q. Du, L. Ju, X. Li, and Z. Qiao. Maximum bound principles for a class of semilinear parabolic equations and exponential time-differencing schemes.SIAM Review, 63(2):317–359, 2021
2021
-
[15]
H. Egger. Structure preserving approximation of dissipative evolution problems.Numerische Mathematik, 143:85–106, 2019. 34
2019
-
[16]
C. M. Elliott and A. M. Stuart. The global dynamics of discrete semilinear parabolic equations. SIAM Journal on Numerical Analysis, 30(6):1622–1663, 1993
1993
-
[17]
D. J. Eyre. Unconditionally gradient stable time marching the Cahn–Hilliard equation.MRS Online Proceedings Library, 529:39–46, 1998
1998
-
[18]
Furihata and T
D. Furihata and T. Matsuo.Discrete Variational Derivative Method: A Structure-Preserving Numerical Method for Partial Differential Equations. CRC Press, 2011
2011
-
[19]
Y. Gong, Q. Hong, and Q. Wang. Supplementary variable method for thermodynamically consistent partial differential equations.Computer Methods in Applied Mechanics and Engi- neering, 381:113909, 2021
2021
-
[20]
Gong and J
Y. Gong and J. Zhao. Energy-stable Runge–Kutta schemes for gradient flow models using the energy quadratization approach.Applied Mathematics Letters, 94:224–231, 2019
2019
-
[21]
Guill´ en-Gonz´ alez and G
F. Guill´ en-Gonz´ alez and G. Tierra. Second order schemes and time-step adaptivity for Allen– Cahn and Cahn–Hilliard models.Computers and Mathematics with Applications, 68(8):821– 846, 2014
2014
-
[22]
D. Hou, Y. Ning, and C. Zhang. An efficient and robust Lagrange multiplier approach with a penalty term for phase-field models.Journal of Computational Physics, 488:112236, 2023
2023
-
[23]
Z. Hu, S. M. Wise, C. Wang, and J. S. Lowengrub. Stable and efficient finite-difference nonlinear-multigrid schemes for the phase field crystal equation.Journal of Computational Physics, 228(15):5323–5339, 2009
2009
-
[24]
Huang, W
Q.-A. Huang, W. Jiang, J. Z. Yang, and C. Yuan. A weighted scalar auxiliary variable method for solving gradient flows: Bridging the nonlinear energy-based and Lagrange multiplier ap- proaches.Journal of Scientific Computing, 106(1):16, 2025
2025
-
[25]
Jiang, Z
M. Jiang, Z. Zhang, and J. Zhao. Improving the accuracy and consistency of the scalar auxiliary variable (SAV) method with relaxation.Journal of Computational Physics, 456:110954, 2022
2022
-
[26]
Jiang and J
M. Jiang and J. Zhao. Linear relaxation schemes for the Allen–Cahn-type and Cahn–Hilliard- type phase field models.Applied Mathematics Letters, 137:108477, 2023
2023
-
[27]
Second order linear energy stable schemes for Allen-Cahn equations with nonlocal constraints.Journal of Scientific Computing, 80(1):500–537, 2019
Xiaobo Jing, Jun Li, Xueping Zhao, and Qi Wang. Second order linear energy stable schemes for Allen-Cahn equations with nonlocal constraints.Journal of Scientific Computing, 80(1):500–537, 2019
2019
-
[28]
L. Ju, X. Li, Z. Qiao, and H. Zhang. Energy stability and error estimates of exponential time differencing schemes for the epitaxial growth model without slope selection.Mathematics of Computation, 87(312):1859–1885, 2018
2018
-
[29]
Karma and W
A. Karma and W. Rappel. Quantitative phase-field modeling of dendritic growth in two and three dimensions.Physical Review E, 57:4323–4349, 1998
1998
-
[30]
Li and Z
D. Li and Z. Qiao. On second order semi-implicit Fourier spectral methods for 2D Cahn– Hilliard equations.Journal of Scientific Computing, 70(1):301–341, 2017
2017
-
[31]
D. Li, Z. Qiao, and T. Tang. Characterizing the stabilization size for semi-implicit Fourier- spectral method to phase field equations.SIAM Journal on Numerical Analysis, 54(3):1653– 1681, 2016. 35
2016
-
[32]
Liu and J
C. Liu and J. Shen. A phase field model for the mixture of two incompressible fluids and its approximation by a Fourier-spectral method.Physica D: Nonlinear Phenomena, 179(3– 4):211–228, 2003
2003
-
[33]
Liu and X
Z. Liu and X. Li. A novel Lagrange multiplier approach with relaxation for gradient flows. CSIAM Transactions on Applied Mathematics, 5(1):110–141, 2024
2024
-
[34]
Lowengrub and L
J. Lowengrub and L. Truskinovsky. Quasi-incompressible Cahn–Hilliard fluids and topologi- cal transitions.Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 454(1978):2617–2654, 1998
1978
-
[35]
R. I. McLachlan, G. R. W. Quispel, and N. Robidoux. Geometric integration using discrete gradients.Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 357(1754):1021–1045, 1999
1999
-
[36]
Z. Qiao, Z. Zhang, and T. Tang. An adaptive time-stepping strategy for the molecular beam epitaxy models.SIAM Journal on Scientific Computing, 33(3):1395–1414, 2011
2011
-
[37]
J. Shen, C. Wang, X. Wang, and S. M. Wise. Second-order convex splitting schemes for gradient flows with Ehrlich–Schwoebel type energy: Application to thin film epitaxy.SIAM Journal on Numerical Analysis, 50(1):105–125, 2012
2012
-
[38]
J. Shen, J. Xu, and J. Yang. The scalar auxiliary variable (SAV) approach for gradient flows. Journal of Computational Physics, 353:407–416, 2018
2018
-
[39]
J. Shen, J. Xu, and J. Yang. A new class of efficient and robust energy stable schemes for gradient flows.SIAM Review, 61(3):474–506, 2019
2019
-
[40]
Shen and X
J. Shen and X. Yang. Numerical approximations of Allen–Cahn and Cahn–Hilliard equations. Discrete and Continuous Dynamical Systems, 28(4):1669–1691, 2010
2010
-
[41]
Wang and H
L. Wang and H. Yu. On efficient second order stabilized semi-implicit schemes for the Cahn– Hilliard phase-field equation.Journal of Scientific Computing, 77(2):1185–1209, 2018
2018
-
[42]
S. Wang, W. Wang, and J. Li. An efficient dynamically regularized Lagrange multiplier method for the incompressible MHD equations.Communications in Nonlinear Science and Numerical Simulation, page 109235, 2025
2025
-
[43]
S. L. Wang, R. F. Sekerka, A. A. Wheeler, B. T. Murray, S. R. Coriell, R. J. Braun, and G. B. McFadden. Thermodynamically-consistent phase-field models for solidification.Physica D: Nonlinear Phenomena, 69:189–200, 1993
1993
-
[44]
S. M. Wise, C. Wang, and J. S. Lowengrub. An energy-stable and convergent finite-difference scheme for the phase field crystal equation.SIAM Journal on Numerical Analysis, 47(3):2269– 2288, 2009
2009
-
[45]
Xu and T
C. Xu and T. Tang. Stability analysis of large time-stepping methods for epitaxial growth models.SIAM Journal on Numerical Analysis, 44(4):1759–1779, 2006
2006
-
[46]
X. Yang. Linear, first and second-order, unconditionally energy stable numerical schemes for the phase field model of homopolymer blends.Journal of Computational Physics, 327:294–316, 2016. 36
2016
-
[47]
X. Yang, J. Zhao, and Q. Wang. Numerical approximations for the molecular beam epitaxial growth model based on the invariant energy quadratization method.Journal of Computational Physics, 333:104–127, 2017
2017
-
[48]
X. Yang, J. Zhao, Q. Wang, and J. Shen. Numerical approximations for a three-components Cahn–Hilliard phase-field model based on the invariant energy quadratization method.Math- ematical Models and Methods in Applied Sciences, 27(11):1993–2030, 2017
1993
-
[49]
Zhang, J
G. Zhang, J. Li, and Q.-A. Huang. A class of unconditionally energy stable relaxation schemes for gradient flows.Mathematics and Computers in Simulation, 218:235–247, 2024
2024
-
[50]
Structure-preserving, energy stable numerical schemes for a liquid thin film coarsening model.SIAM Journal on Scientific Computing, 43(2):A1248–A1272, 2021
Juan Zhang, Cheng Wang, Steven M Wise, and Zhengru Zhang. Structure-preserving, energy stable numerical schemes for a liquid thin film coarsening model.SIAM Journal on Scientific Computing, 43(2):A1248–A1272, 2021
2021
-
[51]
Zhang and Z
Z. Zhang and Z. Qiao. An adaptive time-stepping strategy for the Cahn–Hilliard equation. Communications in Computational Physics, 11(4):1261–1278, 2012
2012
-
[52]
J. Zhao. A revisit of the energy quadratization method with a relaxation technique.Applied Mathematics Letters, 120:107331, 2021
2021
-
[53]
J. Zhao, Q. Wang, and X. Yang. Numerical approximations for a phase field dendritic crystal growth model based on the invariant energy quadratization approach.International Journal for Numerical Methods in Engineering, 110(3):279–300, 2017
2017
-
[54]
J. Zhao, X. Yang, Y. Gong, X. Zhao, J. Li, X. Yang, and Q. Wang. A general strategy for numerical approximations of thermodynamically consistent nonequilibrium models–part I: Thermodynamical systems.International Journal of Numerical Analysis and Modeling, 15(6):884–918, 2018. 37
2018
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.