# \[LinearSolve\] Inexact error in solving 4x4 linear system of equations
**URL:** https://discourse.julialang.org/t/linearsolve-inexact-error-in-solving-4x4-linear-system-of-equations/88404
**Category:** Specific Domains
**Tags:** linearsolve
**Created:** [October 7, 2022, 2:28pm UTC](https://discourse.julialang.org/t/linearsolve-inexact-error-in-solving-4x4-linear-system-of-equations/88404 "2022-10-07T14:28:23Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@TheLateKronos](https://discourse.julialang.org/u/TheLateKronos)
#### Post date: [October 7, 2022, 2:28pm UTC](https://discourse.julialang.org/t/linearsolve-inexact-error-in-solving-4x4-linear-system-of-equations/88404/1 "2022-10-07T14:28:23Z")
I have this issue in solving a simple set of equations:
```julia
julia> using LinearSolve
julia> let
A = [1.0 0.0 -1.0 0.0
0.0 -3152.28 0.0 3152.28
0.388658 0.921382 -1.76854 -1.45868
0.921382 -0.388658 1.45868 1.76854]
b = [0, 0, 1, 0]
prob = LinearProblem(A, b)
solve(prob)
end
ERROR: InexactError: Int64(3.8064439666352263)
Stacktrace:
[1] Int64
@ ./float.jl:788 [inlined]
[2] convert
@ ./number.jl:7 [inlined]
[3] setindex!
@ ./array.jl:966 [inlined]
[4] ldiv!(A::LinearAlgebra.UpperTriangular{Float64, Matrix{Float64}}, b::Vector{Int64})
@ LinearAlgebra ~/.julia/juliaup/julia-1.8.2+0.x64/share/julia/stdlib/v1.8/LinearAlgebra/src/triangular.jl:1200
[5] ldiv!(A::LinearAlgebra.LU{Float64, Matrix{Float64}, Vector{Int64}}, B::Vector{Int64})
@ LinearAlgebra ~/.julia/juliaup/julia-1.8.2+0.x64/share/julia/stdlib/v1.8/LinearAlgebra/src/lu.jl:409
[6] _ldiv!
@ ~/.julia/packages/LinearSolve/E7qHt/src/factorization.jl:5 [inlined]
[7] #solve#6
@ ~/.julia/packages/LinearSolve/E7qHt/src/factorization.jl:21 [inlined]
[8] solve(cache::LinearSolve.LinearCache{Matrix{Float64}, Vector{Int64}, Vector{Int64}, SciMLBase.NullParameters, Nothing, LinearAlgebra.LU{Float64, Matrix{Float64}, Vector{Int64}}, IterativeSolvers.Identity, IterativeSolvers.Identity, Float64, Nothing}, alg::GenericLUFactorization{LinearAlgebra.RowMaximum})
@ LinearSolve ~/.julia/packages/LinearSolve/E7qHt/src/factorization.jl:16
[9] solve(::LinearSolve.LinearCache{Matrix{Float64}, Vector{Int64}, Vector{Int64}, SciMLBase.NullParameters, Nothing, LinearAlgebra.LU{Float64, Matrix{Float64}, Vector{Int64}}, IterativeSolvers.Identity, IterativeSolvers.Identity, Float64, Nothing}, ::Nothing; assumptions::LinearSolve.OperatorAssumptions{Nothing}, kwargs::Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
@ LinearSolve ~/.julia/packages/LinearSolve/E7qHt/src/default.jl:145
[10] solve
@ ~/.julia/packages/LinearSolve/E7qHt/src/default.jl:141 [inlined]
[11] #solve#5
@ ~/.julia/packages/LinearSolve/E7qHt/src/common.jl:158 [inlined]
[12] solve(::LinearSolve.LinearCache{Matrix{Float64}, Vector{Int64}, Vector{Int64}, SciMLBase.NullParameters, Nothing, LinearAlgebra.LU{Float64, Matrix{Float64}, Vector{Int64}}, IterativeSolvers.Identity, IterativeSolvers.Identity, Float64, Nothing})
@ LinearSolve ~/.julia/packages/LinearSolve/E7qHt/src/common.jl:157
[13] solve(::LinearProblem{Nothing, true, Matrix{Float64}, Vector{Int64}, SciMLBase.NullParameters, Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}}}; kwargs::Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
@ LinearSolve ~/.julia/packages/LinearSolve/E7qHt/src/common.jl:148
[14] solve(::LinearProblem{Nothing, true, Matrix{Float64}, Vector{Int64}, SciMLBase.NullParameters, Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}}})
@ LinearSolve ~/.julia/packages/LinearSolve/E7qHt/src/common.jl:147
[15] top-level scope
@ REPL[2]:8
(@v1.8) pkg> st LinearSolve
Status `~/.julia/environments/v1.8/Project.toml`
[7ed4a6bd] LinearSolve v1.26.1
julia> versioninfo()
Julia Version 1.8.2
Commit 36034abf260 (2022-09-29 15:21 UTC)
Platform Info:
OS: Linux (x86_64-linux-gnu)
CPU: 8 × Intel(R) Core(TM) i5-8265U CPU @ 1.60GHz
WORD_SIZE: 64
LIBM: libopenlibm
LLVM: libLLVM-13.0.1 (ORCJIT, skylake)
Threads: 1 on 8 virtual cores
```
Anyone knows what goes wrong?
---
### Author:  [@Oscar\_Smith](https://discourse.julialang.org/u/Oscar_Smith)
#### Post date: [October 7, 2022, 2:35pm UTC](https://discourse.julialang.org/t/linearsolve-inexact-error-in-solving-4x4-linear-system-of-equations/88404/2 "2022-10-07T14:35:10Z")
make `b = Float64[0, 0, 1, 0]` right now. you are to store the solution in a `Vector{Int}` but the solution isn’t integral.
---
### Author:  [@TheLateKronos](https://discourse.julialang.org/u/TheLateKronos)
#### Post date: [October 7, 2022, 3:20pm UTC](https://discourse.julialang.org/t/linearsolve-inexact-error-in-solving-4x4-linear-system-of-equations/88404/3 "2022-10-07T15:20:29Z")
Thanks, that fixed it! Maybe a more helpful error could be provided?
---
### Author:  [@Oscar\_Smith](https://discourse.julialang.org/u/Oscar_Smith)
#### Post date: [October 7, 2022, 3:32pm UTC](https://discourse.julialang.org/t/linearsolve-inexact-error-in-solving-4x4-linear-system-of-equations/88404/4 "2022-10-07T15:32:28Z")
probably. want to file an issue?
---
### Author:  [@TheLateKronos](https://discourse.julialang.org/u/TheLateKronos)
#### Post date: [October 7, 2022, 3:40pm UTC](https://discourse.julialang.org/t/linearsolve-inexact-error-in-solving-4x4-linear-system-of-equations/88404/5 "2022-10-07T15:40:06Z")
Sure 🙂