# NaN Values for j \> 1700 in Quantum Fisher Information Calculation using QuantumOptics

**URL:** <https://discourse.julialang.org/t/nan-values-for-j-1700-in-quantum-fisher-information-calculation-using-quantumoptics/118923>\
**Category:** Quantum\
**Tags:** question, package\
**Created:** [September 2, 2024, 3:51am UTC](https://discourse.julialang.org/t/nan-values-for-j-1700-in-quantum-fisher-information-calculation-using-quantumoptics/118923 "2024-09-02T03:51:24Z")\
**Posts on this page:** 1\
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**Author:** ![abraemer](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/abraemer/32/51403_2.png) [@abraemer](https://discourse.julialang.org/u/abraemer)\
**Post date:** [September 2, 2024, 4:53am UTC](https://discourse.julialang.org/t/nan-values-for-j-1700-in-quantum-fisher-information-calculation-using-quantumoptics/118923/2 "2024-09-02T04:53:48Z")

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Hey there 🙂  
Please have look at

> [@Please read: make it easier to help you](https://discourse.julialang.org/t/please-read-make-it-easier-to-help-you/14757):
>
> Welcome to the Julia Discourse! We are enthusiastic about helping Julia programmers, both beginner and experienced. This public service announcement (PSA) outlines best practices when asking for help. Following these points makes it easier for us to help you and more likely you’ll get a prompt, useful answer. Keywords are highlighted to make it easier to refer to specific points. Choose a descriptive title that captures the key part of your question, eg “plots with multiple axes” instead of …

And enclose the code you posted in triple backticks `````  
Also your Julia version is rather old. I’d recommend updating to the current version 1.10.5 (I don’t think this causes your problems but it’s better to use a supported version anyways).

Can you please also provide some sample output where the vector breaks down? Is it just the vector that (over time) gets NaNs or do the Hamiltonians contains NaNs from the beginning?

Try updating your KrylovKit.jl since your are 2 versions behind. Perhaps that helps already. Otherwise try increasing the Krylov dimension.

The renormalization step in your loop should in principle be uncessary. If the norm changes (more than a couple `eps`) during the Krylov propagation then went wrong already because it was not unitary.

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