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Introducing iFluid: a numerical framework for solving hydrodynamical equations in integrable models

by Frederik S. Møller, Jörg Schmiedmayer

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Submission summary

Authors (as registered SciPost users): Frederik Skovbo Møller · Jörg Schmiedmayer
Submission information
Preprint Link:  (pdf)
Date accepted: 2020-03-10
Date submitted: 2020-01-09 01:00
Submitted by: Møller, Frederik Skovbo
Submitted to: SciPost Physics
Ontological classification
Academic field: Physics
  • Condensed Matter Physics - Computational
Approach: Computational


We present an open-source Matlab framework, titled iFluid, for simulating the dynamics of integrable models using the theory of generalized hydrodynamics (GHD). The framework provides an intuitive interface, enabling users to define and solve problems in a few lines of code. Moreover, iFluid can be extended to encompass any integrable model, and the algorithms for solving the GHD equations can be fully customized. We demonstrate how to use iFluid by solving the dynamics of three distinct systems: (i) The quantum Newton's cradle of the Lieb-Liniger model, (ii) a gradual field release in the XXZ-chain, and (iii) a partitioning protocol in the relativistic sinh-Gordon model.

Published as SciPost Phys. 8, 041 (2020)

Reports on this Submission

Anonymous Report 2 on 2020-3-5 (Invited Report)

  • Cite as: Anonymous, Report on arXiv:2001.02547v1, delivered 2020-03-04, doi: 10.21468/SciPost.Report.1553


- This work is timely as the dynamics of integrable systems is a topic of intensive experimental study, and this package automates a lot of GHD, thus making it easy for other experimental groups to compare their results to GHD.

- The introduction of spacetime inhomogeneities is a great strength as these are usually experimentally relevant.

- The introduction to GHD is admirably clear.

- For what it's worth I do not entirely agree with the other referee about MATLAB. Especially given the prospect that this work will be widely adopted by experimental groups, I think the choice of language is appropriate.


I do not see any major weaknesses (though as the other referee points out there is room for extension in various directions).


I recommend publication as is.

  • validity: high
  • significance: good
  • originality: good
  • clarity: top
  • formatting: excellent
  • grammar: excellent

Anonymous Report 1 on 2020-3-3 (Invited Report)

  • Cite as: Anonymous, Report on arXiv:2001.02547v1, delivered 2020-03-03, doi: 10.21468/SciPost.Report.1551


1- First open source GHD (generalized hydrodynamics) code
2- More models can be added easily
3- Appears to be relatively easy to use


1- Matlab (proprietary language) is an unfortunate choice for an open-source project. Python or Julia would have been much more appropriate.
2- More methods for solving GHD equations could have been included, such as the flea gas.


In this paper, the authors introduce an open-source Matlab code to simulate the non-equilibrium dynamics of integrable systems using the recently introduced framework of generalized hydrodynamics (GHD). The current version of the code can solve the dynamics of the Lieb-Liniger model, XXZ spin chain in the gapped regime, and of the sinh-Gordon model; in arbitrary (but smooth) time and position-dependent potential.

I believe this is a valuable contribution as it should make GHD a lot more accessible. The code seems to be easy to use and I expect it will greatly benefit the community. The code is modular and other integrable models or other solvers can be implemented. The paper is well-written and easy to read, and the examples nicely illustrate the functionalities of the code. It is unfortunate that the authors chose Matlab -- a proprietary programming language -- for this open source project. I'm hoping to see a C++, Julia or Python version in the future.

Requested changes

I am recommending publication as is.

  • validity: top
  • significance: good
  • originality: good
  • clarity: top
  • formatting: excellent
  • grammar: excellent

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