# Can views function on diag?
**URL:** https://discourse.julialang.org/t/can-views-function-on-diag/128943
**Category:** General Usage
**Tags:** linearalgebra, views, feature-request
**Created:** [May 13, 2025, 2:35am UTC](https://discourse.julialang.org/t/can-views-function-on-diag/128943 "2025-05-13T02:35:47Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@WalterMadelim](https://discourse.julialang.org/u/WalterMadelim)
#### Post date: [May 13, 2025, 2:35am UTC](https://discourse.julialang.org/t/can-views-function-on-diag/128943/1 "2025-05-13T02:35:47Z")
Diagonal vector is a central vector that can be sliced from a `Matrix`, can it be `view`ed?
```julia
julia> using LinearAlgebra
julia> A = rand(-9:9, 2, 2)
2×2 Matrix{Int64}:
-1 6
6 -9
julia> @views d = diag(A)
2-element Vector{Int64}:
-1
-9
julia> d .= 0 # set the diagonals to zero
2-element Vector{Int64}:
0
0
julia> A # it doesn't work
2×2 Matrix{Int64}:
-1 6
6 -9
```
If it functions, it could also be used to, e.g. make a matrix become diagonally dominant, become posdef etc.
---
### Author:  [@karei](https://discourse.julialang.org/u/karei)
#### Post date: [May 13, 2025, 3:06am UTC](https://discourse.julialang.org/t/can-views-function-on-diag/128943/2 "2025-05-13T03:06:21Z")
```julia
julia> A = rand(-9:9, 2, 2)
2×2 Matrix{Int64}:
-5 -2
-1 0
julia> diagidx=[CartesianIndex(i,i) for i=1:2]
2-element Vector{CartesianIndex{2}}:
CartesianIndex(1, 1)
CartesianIndex(2, 2)
julia> view(A,diagidx)
2-element view(::Matrix{Int64}, CartesianIndex{2}[CartesianIndex(1, 1), CartesianIndex(2, 2)]) with eltype Int64:
-5
0
```
The `diag` function creates a new vector, so that method won’t work.
---
### Author:  [@danielwe](https://discourse.julialang.org/u/danielwe)
#### Post date: [May 13, 2025, 3:17am UTC](https://discourse.julialang.org/t/can-views-function-on-diag/128943/3 "2025-05-13T03:17:22Z")
LinearAlgebra.jl provides the `diagind` function so you don’t have to build `diagidx` yourself, and it returns a unit range instead of a vector if possible such that you get a manifestly strided view:
```julia
julia> using LinearAlgebra
julia> A = rand(-9:9, 2, 2)
2×2 Matrix{Int64}:
4 -4
-4 0
julia> @view A[diagind(A)]
2-element view(::Vector{Int64}, 1:3:4) with eltype Int64:
4
0
```
---
### Author:  [@mcabbott](https://discourse.julialang.org/u/mcabbott)
#### Post date: [May 13, 2025, 3:54am UTC](https://discourse.julialang.org/t/can-views-function-on-diag/128943/4 "2025-05-13T03:54:18Z")
Julia 1.12 also has `diagview`, which is basically `@view A[diagind(A)]`.