# ERROR: type Tuple has no field values

**URL:** <https://discourse.julialang.org/t/error-type-tuple-has-no-field-values/100775>\
**Category:** New to Julia\
**Tags:** question\
**Created:** [June 24, 2023, 8:43am UTC](https://discourse.julialang.org/t/error-type-tuple-has-no-field-values/100775 "2023-06-24T08:43:29Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Mingyuan1231](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mingyuan1231/32/51012_2.png) [@Mingyuan1231](https://discourse.julialang.org/u/Mingyuan1231)\
**Post date:** [June 24, 2023, 8:43am UTC](https://discourse.julialang.org/t/error-type-tuple-has-no-field-values/100775/1 "2023-06-24T08:43:29Z")

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I’m trying to simulate a projection measurement of quantum system, here is the code involving error

‘’’

# Calculate eigenvalues and eigenvectors

eigen = eigs(X1.data)  
eigenvalues = eigen.values  
eigenvectors = eigen.vectors  
‘’’

X1 is a four-mode operator, the error happens at the “eigenvalues=eigen.values”, and here is the error message:

ERROR: type Tuple has no field values  
Stacktrace:  
[1] getproperty(x::Tuple{Vector{ComplexF64}, Matrix{ComplexF64}, Int64, Int64, Int64, Vector{ComplexF64}}, f::Symbol)

I don’t understand what caused this error and how could I fix this?

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<div class="post-metadata">

**Author:** ![GunnarFarneback](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/gunnarfarneback/32/1827_2.png) [@GunnarFarneback](https://discourse.julialang.org/u/GunnarFarneback)\
**Post date:** [June 24, 2023, 9:03am UTC](https://discourse.julialang.org/t/error-type-tuple-has-no-field-values/100775/2 "2023-06-24T09:03:50Z")

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> [@Mingyuan1231](#):
>
> eigen = eigs(X1.data)

Which package is `eigs` coming from and is its docstring saying that you should extract eigenvalues with `.values`? My best guess is that you’re supposed to do

```julia
eigenvalues, eigenvectors = eigs(X1.data)

```

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<div class="post-metadata">

**Author:** ![Mingyuan1231](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mingyuan1231/32/51012_2.png) [@Mingyuan1231](https://discourse.julialang.org/u/Mingyuan1231)\
**Post date:** [June 24, 2023, 9:21am UTC](https://discourse.julialang.org/t/error-type-tuple-has-no-field-values/100775/3 "2023-06-24T09:21:04Z")

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Oh! It works for now! Thank you so much! eigs is from Arpack, I was using LinearAlgebra, but it doesn’t allow me to, I guess that’s because the structure of my operator, and the error message suggest me to use eigs from Arpack so I use it.