# ITensor Development **URL:** https://itensor.discourse.group/c/itensor-development/7.md [Latest](https://itensor.discourse.group/latest.md) · [Categories](https://itensor.discourse.group/categories.md) · [Tags](https://itensor.discourse.group/tags.md) --- ## [About the ITensor Development category](https://itensor.discourse.group/t/about-the-itensor-development-category/16)
**Author:** [@miles](https://itensor.discourse.group/u/miles)\ **Replies:** 0
Discussion of the development and design of the ITensor software. Please read the our guide to using the forum before posting, to make it easier for us to help you! --- ## [\[BUG\] Repeated HDF5 read of MPS becomes increasingly slow, apparently related to GC](https://itensor.discourse.group/t/bug-repeated-hdf5-read-of-mps-becomes-increasingly-slow-apparently-related-to-gc/2639)
**Author:** [@JBTouchais](https://itensor.discourse.group/u/JBTouchais)\ **Replies:** 3\ **Last updated:** [September 28, 2026, 7:51am UTC](https://itensor.discourse.group/t/bug-repeated-hdf5-read-of-mps-becomes-increasingly-slow-apparently-related-to-gc/2639 "2026-09-28T07:51:31Z")
Description of issue : Repeated use of HDF5.write(parent::Union{HDF5.File, HDF5.Group}, name::AbstractString, M::MPS) or HDF5.read(parent::Union{HDF5.File, HDF5.Group}, name::AbstractString, ::Type{MPS}) on the same file… --- ## [ATTNs in ITensorNetworks](https://itensor.discourse.group/t/attns-in-itensornetworks/2526)
**Author:** [@Liftuck](https://itensor.discourse.group/u/Liftuck)\ **Replies:** 4\ **Last updated:** [November 11, 2025, 5:17pm UTC](https://itensor.discourse.group/t/attns-in-itensornetworks/2526 "2025-11-11T17:17:21Z")
Hi, are there Plans to include augmented Tree Tensor Networks in the ITensor Networks library at some point? Might there (I see how this is an anoying question) already be an approximate time frame if so? --- ## [Inquiry about PBC-optimized DMRG support in ITensor](https://itensor.discourse.group/t/inquiry-about-pbc-optimized-dmrg-support-in-itensor/2506)
**Author:** [@UynajGI](https://itensor.discourse.group/u/UynajGI)\ **Replies:** 2\ **Last updated:** [November 10, 2025, 5:09pm UTC](https://itensor.discourse.group/t/inquiry-about-pbc-optimized-dmrg-support-in-itensor/2506 "2025-11-10T17:09:59Z")
Hi everyone, I’m working on DMRG simulations of 1D quantum systems with periodic boundary conditions (PBC), and I’m aware that standard DMRG suffers from reduced accuracy and efficiency for PBC due to the long-range bon… --- ## [Would it be possible to enhance subtyping in ITensorMPS?](https://itensor.discourse.group/t/would-it-be-possible-to-enhance-subtyping-in-itensormps/2327)
**Author:** [@VinceNeede](https://itensor.discourse.group/u/VinceNeede)\ **Replies:** 4\ **Last updated:** [April 1, 2025, 5:28pm UTC](https://itensor.discourse.group/t/would-it-be-possible-to-enhance-subtyping-in-itensormps/2327 "2025-04-01T17:28:10Z")
Hi all. I wanted to ask whether it was possible, and your opinion about it, to add a type node between AbstractMPS and the concrete types MPS and MPO. I mean something like this: abstract type AbstractNSitesMPO{N} end … --- ## [make \`MPS\` and \`OpSum\` forward kwargs to \`state\` and \`op\`](https://itensor.discourse.group/t/make-mps-and-opsum-forward-kwargs-to-state-and-op/2285)
**Author:** [@VinceNeede](https://itensor.discourse.group/u/VinceNeede)\ **Replies:** 0\ **Last updated:** [March 6, 2025, 12:22am UTC](https://itensor.discourse.group/t/make-mps-and-opsum-forward-kwargs-to-state-and-op/2285 "2025-03-06T00:22:16Z")
It is not clear if something like that is possible or not. About OpSum, it seems that after this Issue PastaQ.jl/Issue#247 it is possible to pass multi site operators and parameters, So I can write something like sites… --- ## [LinearMaps and ITensors incompatibility?](https://itensor.discourse.group/t/linearmaps-and-itensors-incompatibility/2216)
**Author:** [@srwhite](https://itensor.discourse.group/u/srwhite)\ **Replies:** 7\ **Last updated:** [February 7, 2025, 4:05pm UTC](https://itensor.discourse.group/t/linearmaps-and-itensors-incompatibility/2216 "2025-02-07T16:05:41Z")
I am encountering strange incompatibility between LinearMaps and ITensors. I have LinearMaps v3.11.3 and ITensors v0.7.11. “using” hangs when I try to do both: faraday% julia \_ \_ \_ ()\_ | Documentation: htt… --- ## [SU(2) implementation](https://itensor.discourse.group/t/su-2-implementation/2127)
**Author:** [@dfelmanl](https://itensor.discourse.group/u/dfelmanl)\ **Replies:** 3\ **Last updated:** [January 8, 2025, 7:03pm UTC](https://itensor.discourse.group/t/su-2-implementation/2127 "2025-01-08T19:03:16Z")
Hi, I am interested in working with non-abelian symmetries imposed on TN, specifically SU(2). I am aware that ITensor is planning to develop this support, but is there an expected delivery for the feature? Thank you i… --- ## [Handle duplicate index](https://itensor.discourse.group/t/handle-duplicate-index/2188)
**Author:** [@subrata](https://itensor.discourse.group/u/subrata)\ **Replies:** 2\ **Last updated:** [December 29, 2024, 7:35pm UTC](https://itensor.discourse.group/t/handle-duplicate-index/2188 "2024-12-29T19:35:51Z")
A correct way to define a ITensor is the following using ITensors i = Index(2) j = Index(2) A = random\_itensor(i, j) Now what if I do the following A = random\_itensor(i,i) It does not raise any warning or error. Bu… --- ## [VUMPS, Hopping term sign is important?](https://itensor.discourse.group/t/vumps-hopping-term-sign-is-important/2150)
**Author:** [@sunam](https://itensor.discourse.group/u/sunam)\ **Replies:** 4\ **Last updated:** [December 12, 2024, 2:14am UTC](https://itensor.discourse.group/t/vumps-hopping-term-sign-is-important/2150 "2024-12-12T02:14:14Z")
Sign of hopping term of Hamiltonian is important in VUMPS or DMRG? When the Hamiltonian is simply given by the hopping term and the U term, Is there a difference when the sign of the hopping term is positive versus neg… --- ## [Does ITensor support quantum chemistry (molecular) Hamiltonian?](https://itensor.discourse.group/t/does-itensor-support-quantum-chemistry-molecular-hamiltonian/1987)
**Author:** [@alorium](https://itensor.discourse.group/u/alorium)\ **Replies:** 2\ **Last updated:** [September 15, 2024, 2:53am UTC](https://itensor.discourse.group/t/does-itensor-support-quantum-chemistry-molecular-hamiltonian/1987 "2024-09-15T02:53:03Z")
If not, any plan to develop quantum chemistry capabilities? --- ## [pull request on Github](https://itensor.discourse.group/t/pull-request-on-github/334)
**Author:** [@MaxSilvester](https://itensor.discourse.group/u/MaxSilvester)\ **Replies:** 2\ **Last updated:** [August 30, 2024, 5:27pm UTC](https://itensor.discourse.group/t/pull-request-on-github/334 "2024-08-30T17:27:11Z")
My research advisor, Steve White, has suggested that my code for computing the two-site variance be added to the ITensors.jl package. The two-site variance (https://arxiv.org/pdf/1711.01104.pdf) as proposed by Schollwöc… --- ## [Bug in factorize\_qr leading to very slow calls to orthogonalize!](https://itensor.discourse.group/t/bug-in-factorize-qr-leading-to-very-slow-calls-to-orthogonalize/1412)
**Author:** [@srwhite](https://itensor.discourse.group/u/srwhite)\ **Replies:** 12\ **Last updated:** [February 5, 2024, 6:12pm UTC](https://itensor.discourse.group/t/bug-in-factorize-qr-leading-to-very-slow-calls-to-orthogonalize/1412 "2024-02-05T18:12:49Z")
If I factorize a tensor with indices i,j,k, and I specify i,j as the left indices, then the factor L has a new third index, i,j,m. m should not be larger than k. With factorize\_qr, it can be larger than k, but not wi… --- ## [CMake support for iTensor cpp package](https://itensor.discourse.group/t/cmake-support-for-itensor-cpp-package/708)
**Author:** [@fracton](https://itensor.discourse.group/u/fracton)\ **Replies:** 1\ **Last updated:** [March 18, 2023, 5:18pm UTC](https://itensor.discourse.group/t/cmake-support-for-itensor-cpp-package/708 "2023-03-18T17:18:44Z")
Hi, I just started out with iTensor for some simple DMRG calculations. I was just wondering, why the installation for C++ code base uses gnu make and not CMake? Are there any plans to migrate to a CMake installation. --- ## [Julia NDTensors development](https://itensor.discourse.group/t/julia-ndtensors-development/511)
**Author:** [@JanReimers](https://itensor.discourse.group/u/JanReimers)\ **Replies:** 2\ **Last updated:** [November 16, 2022, 9:57pm UTC](https://itensor.discourse.group/t/julia-ndtensors-development/511 "2022-11-16T21:57:30Z")
The AdvancedUsageGuide gives excellent instructions for developing inside ITensors.jl, the secret sauce being command: Pkg.develop(url=“https://github.com/\[MyGitHubForkLocation\]/ITensors.jl”) As part of implementing Bl… --- ## [Future of C++ version of ITensor](https://itensor.discourse.group/t/future-of-c-version-of-itensor/345)
**Author:** [@raffaele](https://itensor.discourse.group/u/raffaele)\ **Replies:** 2\ **Last updated:** [August 29, 2022, 8:51am UTC](https://itensor.discourse.group/t/future-of-c-version-of-itensor/345 "2022-08-29T08:51:02Z")
Dear ITensor Developers, I have read some comments in which ITensor users have been suggested to use the Julia version of the library, rather than the C++. Indeed, it seems that the Julia version, albeit much younger th… --- ## [implement full QR/SVD with QNs preserved](https://itensor.discourse.group/t/implement-full-qr-svd-with-qns-preserved/268)
**Author:** [@Maximus](https://itensor.discourse.group/u/Maximus)\ **Replies:** 2\ **Last updated:** [August 6, 2022, 2:20pm UTC](https://itensor.discourse.group/t/implement-full-qr-svd-with-qns-preserved/268 "2022-08-06T14:20:31Z")
I am aware that full QR and SVD factorizations are not currently supported in ITensors.jl for block-sparse tensors. However, I need this functionality, and would like to tackle the implementation on my own. More specif… --- ## [Doubled / product SiteTypes and matrix product super operators](https://itensor.discourse.group/t/doubled-product-sitetypes-and-matrix-product-super-operators/89)
**Author:** [@DomCRose](https://itensor.discourse.group/u/DomCRose)\ **Replies:** 6\ **Last updated:** [May 18, 2022, 9:30am UTC](https://itensor.discourse.group/t/doubled-product-sitetypes-and-matrix-product-super-operators/89 "2022-05-18T09:30:06Z")
Hi guys, once again, thanks for the great package! We are currently looking into using ITensors (julia) for some open quantum systems (1D) work and trying to figure out what the best way forward for defining super opera… --- ## [will ITensor implement non abelian symmetry in the near future?](https://itensor.discourse.group/t/will-itensor-implement-non-abelian-symmetry-in-the-near-future/134)
**Author:** [@phyjswang](https://itensor.discourse.group/u/phyjswang)\ **Replies:** 3\ **Last updated:** [May 12, 2022, 9:15am UTC](https://itensor.discourse.group/t/will-itensor-implement-non-abelian-symmetry-in-the-near-future/134 "2022-05-12T09:15:00Z")
Dear ITensor developers, ITensor has become a very mature package for DMRG calculations with abelian symmetries. I guess it may be the time for going one step further, by implementing some common non-abelian symmetries …