# Get Cholesky Factors of sparse input matrix in Julia v0.7/1.0

**URL:** <https://discourse.julialang.org/t/get-cholesky-factors-of-sparse-input-matrix-in-julia-v0-7-1-0/13987>\
**Category:** General Usage\
**Tags:** linearalgebra\
**Created:** [August 24, 2018, 10:42am UTC](https://discourse.julialang.org/t/get-cholesky-factors-of-sparse-input-matrix-in-julia-v0-7-1-0/13987 "2018-08-24T10:42:53Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![migarstka](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/migarstka/32/3828_2.png) [@migarstka](https://discourse.julialang.org/u/migarstka)\
**Post date:** [August 24, 2018, 10:42am UTC](https://discourse.julialang.org/t/get-cholesky-factors-of-sparse-input-matrix-in-julia-v0-7-1-0/13987/1 "2018-08-24T10:42:53Z")

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Hi everyone,

is there any way to extract the lower triangular matrix L from the cholesky factorization F of a **sparse** matrix  
`A = L*L'` obtained by

```julia
F = cholesky(A)

```

MWE:

```julia
using LinearAlgebra

# create a sparse random positive definite matrix
A = sprandn(10,10,0.1)
A = A*A'
A = A + 10*Diagonal(ones(10))

F = cholesky(A)

# F.L only returns the SuiteSparse.CHOLMOD Factor

```

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<div class="post-metadata">

**Author:** ![Tamas\_Papp](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tamas_papp/32/25949_2.png) [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)\
**Post date:** [August 24, 2018, 10:44am UTC](https://discourse.julialang.org/t/get-cholesky-factors-of-sparse-input-matrix-in-julia-v0-7-1-0/13987/2 "2018-08-24T10:44:35Z")

</div>

```julia
using LinearAlgebra
m = Matrix(Diagonal(ones(2)))
cholesky(m).L

```

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<div class="post-metadata">

**Author:** ![migarstka](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/migarstka/32/3828_2.png) [@migarstka](https://discourse.julialang.org/u/migarstka)\
**Post date:** [August 24, 2018, 10:45am UTC](https://discourse.julialang.org/t/get-cholesky-factors-of-sparse-input-matrix-in-julia-v0-7-1-0/13987/3 "2018-08-24T10:45:46Z")

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That only works for dense input matrices though

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<div class="post-metadata">

**Author:** ![Tamas\_Papp](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tamas_papp/32/25949_2.png) [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)\
**Post date:** [August 24, 2018, 10:46am UTC](https://discourse.julialang.org/t/get-cholesky-factors-of-sparse-input-matrix-in-julia-v0-7-1-0/13987/4 "2018-08-24T10:46:23Z")

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Please provide a minimal working example.

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<div class="post-metadata">

**Author:** ![chriscoey](https://avatars.discourse-cdn.com/v4/letter/c/3ab097/32.png) [@chriscoey](https://discourse.julialang.org/u/chriscoey)\
**Post date:** [August 24, 2018, 9:36pm UTC](https://discourse.julialang.org/t/get-cholesky-factors-of-sparse-input-matrix-in-julia-v0-7-1-0/13987/5 "2018-08-24T21:36:14Z")

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In Julia 1.1, after `using SparseArrays`, calling `sparse(F.L)` returned a 10×10 SparseMatrixCSC{Float64,Int64} with 19 stored entries