# 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:** 6

<div class="post-metadata">

### Author: ![miles](https://yyz2.discourse-cdn.com/free1/user_avatar/itensor.discourse.group/miles/32/6_2.png) [@miles](https://itensor.discourse.group/u/miles)
#### Post date: [June 13, 2022, 7:00pm UTC](https://itensor.discourse.group/t/constant-shift-in-mps-shift-and-invert-algo/174/6 "2022-06-13T19:00:44Z")

</div>

I believe the `ProjMPS` type would have most of what you need for the last part (projecting the MPS |b\rangle): [https://github.com/ITensor/ITensors.jl/blob/main/src/mps/projmps.jl](https://github.com/ITensor/ITensors.jl/blob/main/src/mps/projmps.jl)

You may need to modify some things though, like the `product` function.

---

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