# Constant shift in MPS shift-and-invert algo

**URL:** https://itensor.discourse.group/t/constant-shift-in-mps-shift-and-invert-algo/174
**Category:** DMRG and Numerical Methods
**Created:** [May 26, 2022, 10:21pm UTC](https://itensor.discourse.group/t/constant-shift-in-mps-shift-and-invert-algo/174 "2022-05-26T22:21:24Z")
**Posts on this page:** 1
**Showing post:** 8

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### Author: ![ray-l](https://yyz2.discourse-cdn.com/free1/user_avatar/itensor.discourse.group/ray-l/32/76_2.png) [@ray-l](https://itensor.discourse.group/u/ray-l)
#### Post date: [September 27, 2022, 3:40am UTC](https://itensor.discourse.group/t/constant-shift-in-mps-shift-and-invert-algo/174/8 "2022-09-27T03:40:20Z")

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Hi miles,

You probably have seen it and working on a solution (or that my new question was formulated badly and if that’s case I do apologize). But I’ve modified the code a bit to do the iterative linear solving, which for the moment does not work.

Just in case, the new question is linked here

> [@Issues using linsolve (cont'd discussion)](https://itensor.discourse.group/t/issues-using-linsolve-contd-discussion/410):
>
> Continuing the discussion from [Constant shift in MPS shift-and-invert algo](https://itensor.discourse.group/t/constant-shift-in-mps-shift-and-invert-algo/174/6): I finally have time to come back to this problem. In short, I’m trying to variationally solve the following linear system: (H - \lambda) |\psi\rangle = |\phi\rangle Or that o--o--o- -o--o--o--o--o--o \<psi| | | | | | | | | | | | o--o--o--o--o--o--o--o--o--o--o H | | | | | | | | | | | o--o--o--o--o--o--o--o--o--o--o H | | | | | | | | | | | o--o--o- …

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_[View the full topic](https://itensor.discourse.group/t/constant-shift-in-mps-shift-and-invert-algo/174)._