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Andreas Mielke

@mielke@ieji.de
mastodon 4.7.3
  • Open on ieji.de

Main research topics:
- Strong correlations, Hubbard model
- Flat bands, Ferromagnetism
- Continuous unitary transformations
- Flow equations
- Stochastic systems
You can find my list of publications on my homepage or on google scholar.

4 Followers
10 Following
14 Posts
Joined January 22, 2025
homepage:
https://www.thphys.uni-heidelberg.de/~mielke/
google scholar:
https://scholar.google.de/citations?user=pI831gEAAAAJ
orcid:
https://orcid.org/0000-0002-1008-5891
Open post
Andreas Mielke @mielke@ieji.de
· 2mo ago
Update of our paper is now available on arXiv! 📄 "The bosonic Hubbard model on a three-dimensional flat band lattice" (arXiv:2604.19703) 🔗 http://arxiv.org/abs/2604.19703 We present a frustration-free bosonic Hubbard model on a 3D flat band lattice, the line graph of the cubic lattice. For the first time (to our knowledge), we observe subextensive ground state entropy in a bosonic lattice model. The result is related to the number of 4-cycle decompositions of the cubic lattice, for which we derive upper and lower bounds. Co-authored with Leon Haag-Fank. Looking forward to your thoughts and discussions! #Physics #Math #CondensedMatter #OpenScience #arXiv
arxiv.org
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Open post
Andreas Mielke @mielke@ieji.de
· 9mo ago

Just in case somebody has a similar problem: I am using #Emacs on #openSUSE 15.6. Since the last update of some openSUSE packages, something is wrong with emacs-gtk (the standard which is started under X11). After some time, esp. after sending two emails (sometimes already after sending one email) emacs takes no further input from the keyboard. My workaround: emacs-x11, which uses LUCID, or emacs-wayland work without errors.

ieji.de

ieji.de

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Open post
Andreas Mielke @mielke@ieji.de
· 18mo ago

Approximately four weeks ago I installed #Emacs and #termux from
https://sourceforge.net/projects/android-ports-for-gnu-emacs/files/termux/
on my Android phone and tablett. After four weeks I can say: Everything works perfectly fine. I use mu4e for email, org, org-roam, elfeed, etc..

It simplifies my workflow a lot. When I read something on my tablett or phone, I can copy and paste tidbits directly into Org Mode notes. Via syncthing, the notes are kept in sync on all devices.

ieji.de

ieji.de

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Open post
Andreas Mielke @mielke@ieji.de
· 20mo ago

@hajovonta@mastodon.online @Atemu@darmstadt.social
In the termux version, most things work fine, besides mu4e I use org-mode, elfeed, ... I was just curious whether you tried something in the Android version. Will give it a try and tell you about the success.

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Open post
Andreas Mielke @mielke@ieji.de
· 20mo ago

@hajovonta@mastodon.online @Atemu@darmstadt.social @emacs
On the other hand, Termux+Emacs can be used with mu4e and some other stuff. Up to now I was not able to figure out whether e.g. mu4e works with the android version. Would be great.

lemmy.ml
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Open post
Andreas Mielke @mielke@ieji.de
· 2mo ago

Update: Our Paper Has Been Accepted for Publication!

Two days ago, I shared an updated version of our latest work on arXiv. Today, I’m thrilled to announce that "The bosonic Hubbard model on a three-dimensional flat band lattice" (arXiv:2604.19703) has been accepted for publication in Reviews in Mathematical Physics by the referees!

A huge thank you to everyone who engaged with our preprint, shared feedback, or simply showed interest in our research. Your input has been invaluable!

📄 Paper Link: https://arxiv.org/abs/2604.19703

Looking forward to your thoughts and discussions!

#MathematicalPhysics #CondensedMatter #Combinatorics #QuantumPhysics #arXiv

The bosonic Hubbard model on a three dimensional flat band lattice
arXiv.org

The bosonic Hubbard model on a three dimensional flat band lattice

The lowest eigenstates of the hopping matrix on the line graph of a cubic lattice with periodic boundary conditions are highly degenerate, they form a lowest flat band. Further, these states are localized. If one considers a repulsive bosonic Hubbard model on this lattice it is possible to construct exact multi-particle ground states simply by putting particles in the localized single particle ground states such that they avoid each other. This can be done up to a certain critical particle numbe

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Open post
Andreas Mielke @mielke@ieji.de
· 3mo ago

Evaluation of the bvars Package for Multivariate Time Series Analysis

Over the past three days, I evaluated the bvars package (Liu, Ramirez Hassan, & Woźniak) for multivariate autoregressive modeling in R. The package is available on CRAN with DOI: 10.32614/CRAN.package.bvars.

Dataset Characteristics:

The evaluation employed 280 multivariate time series datasets, each comprising nine univariate series. Series length varied between 90 and 450 observations. The data consisted of operational metrics from 2022–2024, including purchase orders, schedule lines, material movements (inbound/outbound), sales orders (requested and confirmed quantities), deliveries, and inventory levels across multiple materials. Given their operational origin, these series exhibited substantial stochastic variation, making them appropriate for assessing time series analysis and forecasting methods.

Comparative Performance:

Within each dataset, the nine series exhibited significant lagged cross-correlations. The standard vars package failed to converge or produce valid estimates for approximately 67% of datasets. In contrast, bvars successfully converged for 279 of 280 datasets (99.6% convergence rate). All analyses employed the default configuration of 10,000 MCMC draws, which proved adequate for these datasets. Posterior diagnostics, model validation tests, and forecast assessments all indicated satisfactory model specification and estimation quality.

Conclusion:

These results suggest that bvars offers substantial advantages over traditional VAR methods for highly correlated multivariate time series with substantial noise. I recommend this package for practitioners working with similar operational or business datasets.

I gratefully acknowledge Rui Liu, Andrés Ramirez Hassan, and Tomasz Woźniak for developing this valuable tool.

#RStats #bvars #bsvars

ieji.de

ieji.de

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Open post
Andreas Mielke @mielke@ieji.de
· 5mo ago

Interested in lattice models of strongly interacting bosons?
We (Leon Haag-Fank and myself) got interesting new results for the bosonic Hubbard model on a three-dimensional flat-band lattice, the line graph of the cubic lattice. Among other results we prove that at a critical particle number, the system has a sub-extensive ground state entropy. This occurs often in highly frustrated spin systems but has, to our knowledge, not been observed in a bosonic lattice model.
The problem is related to the number of 4-cycle decompositions of the cubic lattice with periodic boundary conditions, a question that occurs in graph theory.
Here is the link to arxiv.org:
https://arxiv.org/abs/2604.19703
#Physics
#graphtheory
#HubbardModel
#FlatBand
#Entropy

The bosonic Hubbard model on a three dimensional flat band lattice
arXiv.org

The bosonic Hubbard model on a three dimensional flat band lattice

The lowest eigenstates of the hopping matrix on the line graph of a cubic lattice with periodic boundary conditions are highly degenerate, they form a lowest flat band. Further, these states are localized. If one considers a repulsive bosonic Hubbard model on this lattice it is possible to construct exact multi-particle ground states simply by putting particles in the localized single particle ground states such that they avoid each other. This can be done up to a certain critical particle numbe

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Open post
Andreas Mielke @mielke@ieji.de
· 16mo ago

@ericsfraga@fediscience.org @trentskunk@mstdn.social
I use the same setup as eric since years, works perfectly fine. If you want to export the entries in nextcloud to some local ics files, you may use vdirsyncer in addition to org-caldav-sync.

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Open post
Andreas Mielke @mielke@ieji.de
· 18mo ago

@aesthr@wandering.shop okay, second possibility I tried as well: Generate entire pages with figure, text, what ever using the grid library. But then you need to glue those pages together using e.g. pdftk and there will be no navigation like in beamer. Does that help?

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Open post
Andreas Mielke @mielke@ieji.de
· 18mo ago

@aesthr@wandering.shop , I have done similar things for years using R and LaTeX. For each item I generate the plot(s), text and some LaTeX-code which I then bind together via include or input. The include or input statements are also generated by R, so everything is automated. I have produced presentation style reports using the Beamer class or usual reports.

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Open post
Andreas Mielke @mielke@ieji.de
· 20mo ago

@hajovonta@mastodon.online @Atemu@darmstadt.social @emacs
What about org-mode, did you try that?

lemmy.ml
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Open post
Andreas Mielke @mielke@ieji.de
· 20mo ago

@Global_Repercussions@climatejustice.social
Thanks for pointing me to planetary solvency. I have been recently interested in the effect of climate change to ecosystems, studying papers like
https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.19247
or the Dasgupta Review.

nph.onlinelibrary.wiley.com
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Open post
Andreas Mielke @mielke@ieji.de
· 20mo ago

@Global_Repercussions@climatejustice.social
Thanks a lot, worth reading.
I really appreciated the depth and insight of this article on climate change and the risks we face when looking at local consequences. Zoë Schlanger does an excellent job of pointing out the local risks. However, I found the title, "Climate Models Can’t Explain ..." to be a bit misleading. With the new U.S. presidency and its withdrawal from the Paris Agreement, it’s crucial that we recognize the urgency of addressing these risks.

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