# A sparse matrix cannot be indexed by a SVector
**URL:** https://discourse.julialang.org/t/a-sparse-matrix-cannot-be-indexed-by-a-svector/104265
**Category:** General Usage
**Tags:** staticarrays, sparsearrays
**Created:** [September 26, 2023, 2:12pm UTC](https://discourse.julialang.org/t/a-sparse-matrix-cannot-be-indexed-by-a-svector/104265 "2023-09-26T14:12:40Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@pinkie.ljz](https://discourse.julialang.org/u/pinkie.ljz)
#### Post date: [September 26, 2023, 2:12pm UTC](https://discourse.julialang.org/t/a-sparse-matrix-cannot-be-indexed-by-a-svector/104265/1 "2023-09-26T14:12:40Z")
As indicated by the topic, I intend to replace some small matrices with the StaticArrays but the global sparse matrix created by SparseArrays.jl cannot be indexed by a SVector. A simple example is given as follows.
```julia
using SparseArrays
using StaticArrays
A = spzeros(10, 10)
ind1 = SVector(1, 2, 3, 4)
a = @SArray rand(4, 4)
A[ind1, ind1] += a
@show A
```
The error is given in REPL as
```julia
julia> A[ind1,ind1] += a
ERROR: MethodError: no method matching length(::StaticArrays.StaticIndexing{SVector{4, Int64}})
Closest candidates are:
length(::Union{Base.KeySet, Base.ValueIterator})
@ Base abstractdict.jl:58
length(::Union{SparseArrays.FixedSparseVector{Tv, Ti}, SparseVector{Tv, Ti}} where {Tv, Ti})
@ SparseArrays C:\lijinze\julia\share\julia\stdlib\v1.9\SparseArrays\src\sparsevector.jl:95
length(::Union{ZMQ._Message, Base.RefValue{ZMQ._Message}})
@ ZMQ C:\lijinze\julia\packages\packages\ZMQ\lrABE\src\_message.jl:31
...
Stacktrace:
[1] setindex!(A::SparseMatrixCSC{Float64, Int64}, V::SMatrix{4, 4, Float64, 16}, Ix::SVector{4, Int64}, Jx::SVector{4, Int64})
@ SparseArrays C:\users\julia\share\julia\stdlib\v1.9\SparseArrays\src\sparsematrix.jl:3170
[2] top-level scope
@ REPL[24]:1
```
Thanks in advance for tackling this problem.
---
### Author:  [@oheil](https://discourse.julialang.org/u/oheil)
#### Post date: [September 26, 2023, 2:43pm UTC](https://discourse.julialang.org/t/a-sparse-matrix-cannot-be-indexed-by-a-svector/104265/2 "2023-09-26T14:43:35Z")
The sparse matrix A doesn’t hold any values, except for the default value zero (of default type Float64) which isn’t explicitly stored. Accessing any range of indices gives some dots:
```julia
julia> A[ind1, ind1]
4×4 SparseMatrixCSC{Float64, Int64} with 0 stored entries:
⋅ ⋅ ⋅ ⋅
⋅ ⋅ ⋅ ⋅
⋅ ⋅ ⋅ ⋅
⋅ ⋅ ⋅ ⋅
```
Accessing via a single index returns the default value 0.0:
```julia
julia> A[1]
0.0
```
You operation can be written as (see the dot before the +):
```julia
julia> A[ind1,ind1] .+= a
4×4 view(::SparseMatrixCSC{Float64, Int64}, [1, 2, 3, 4], [1, 2, 3, 4]) with eltype Float64 with indices SOneTo(4)×SOneTo(4):
0.396905 0.518507 0.0333795 0.428079
0.105497 0.358759 0.0329777 0.748697
0.495962 0.948462 0.214173 0.55445
0.517173 0.866702 0.91867 0.352342
julia> A
10×10 SparseMatrixCSC{Float64, Int64} with 16 stored entries:
0.396905 0.518507 0.0333795 0.428079 ⋅ ⋅ ⋅ ⋅ ⋅ ⋅
0.105497 0.358759 0.0329777 0.748697 ⋅ ⋅ ⋅ ⋅ ⋅ ⋅
0.495962 0.948462 0.214173 0.55445 ⋅ ⋅ ⋅ ⋅ ⋅ ⋅
0.517173 0.866702 0.91867 0.352342 ⋅ ⋅ ⋅ ⋅ ⋅ ⋅
⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅
⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅
⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅
⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅
⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅
⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅
```
This is a bit of a lack in the documentation of [Sparse Arrays · The Julia Language](https://docs.julialang.org/en/v1/stdlib/SparseArrays/#Sparse-matrix-operations) I would say, where it says:
> Arithmetic operations on sparse matrices also work as they do on dense matrices.
The error message points to a forgotten implementation of method `length(::StaticArrays.StaticIndexing{SVector{4, Int64}})` somewhere, but I don’t have the nerves to look this up for now, and it wouldn’t help you much for your issue.
---
### Author:  [@pinkie.ljz](https://discourse.julialang.org/u/pinkie.ljz)
#### Post date: [September 26, 2023, 3:02pm UTC](https://discourse.julialang.org/t/a-sparse-matrix-cannot-be-indexed-by-a-svector/104265/3 "2023-09-26T15:02:37Z")
Thank you very much! It succeeds in addressing my problem.
---
### Author:  [@Raf](https://discourse.julialang.org/u/Raf)
#### Post date: [September 26, 2023, 3:03pm UTC](https://discourse.julialang.org/t/a-sparse-matrix-cannot-be-indexed-by-a-svector/104265/4 "2023-09-26T15:03:52Z")
This is basically an incorrect return value from `to_indices` in StaticArrays.jl:
>
It’s overriding internals `Base._getindex` but that doesn’t actually work.
>
`StaticIndexing` needs to be `<: AbstractArray` and it needs to define `iterate` and `size` (shockingly not `getindex` but that’s another story…).
Please make an issue for this in StaticArrays.jl
---
### Author:  [@Raf](https://discourse.julialang.org/u/Raf)
#### Post date: [September 26, 2023, 3:18pm UTC](https://discourse.julialang.org/t/a-sparse-matrix-cannot-be-indexed-by-a-svector/104265/5 "2023-09-26T15:18:04Z")
From the `to_indices` docs:
“The returned tuple must only contain either Ints or AbstractArrays of scalar indices that are supported by array A”
StaticArrays.jl is just breaking the interface here.
Issue made here:
>
>
> The \`to\_indices\` docs state that:
> \> The returned tuple must only contain either… Ints or AbstractArrays of scalar indices that are supported by array A
>
> But \`StaticIndexing\` is not either:
>
> https://github.com/JuliaArrays/StaticArrays.jl/blob/217e6f10a01433b8a60b679622065bc8702da923/src/indexing.jl#L213-L221
>
> See discourse:
> https://discourse.julialang.org/t/a-sparse-matrix-cannot-be-indexed-by-a-svector/104265/5