# Constant linear equation d/dt x=Ax with DifferentialEquations.jl
**URL:** https://discourse.julialang.org/t/constant-linear-equation-d-dt-x-ax-with-differentialequations-jl/57532
**Category:** Modelling & Simulations
**Created:** [March 19, 2021, 12:12pm UTC](https://discourse.julialang.org/t/constant-linear-equation-d-dt-x-ax-with-differentialequations-jl/57532 "2021-03-19T12:12:55Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@jamblejoe](https://discourse.julialang.org/u/jamblejoe)
#### Post date: [March 19, 2021, 12:12pm UTC](https://discourse.julialang.org/t/constant-linear-equation-d-dt-x-ax-with-differentialequations-jl/57532/1 "2021-03-19T12:12:55Z")
In [Non-autonomous Linear ODE / Lie Group ODE Solvers · DifferentialEquations.jl](https://diffeq.sciml.ai/stable/solvers/nonautonomous_linear_ode) are examples for solving d/dt x = A(t) x, time-dependent A, or state dependent A(x), d/dt x = A(x)x, but no example for just constant A. How do I solve d/dt x=Ax for a constant matrix A with `LinearExponential` solver?
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### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [March 19, 2021, 12:44pm UTC](https://discourse.julialang.org/t/constant-linear-equation-d-dt-x-ax-with-differentialequations-jl/57532/2 "2021-03-19T12:44:37Z")
Something like:
```julia
using OrdinaryDiffEq
_A = [2 -1;-3 -5]/5
A = DiffEqArrayOperator(_A)
prob = ODEProblem(A, [1.0,-1.0], (1.0, 6.0))
sol = solve(prob, LinearExponential())
```
should do it. PR to the docs if you think that’s a good addition.
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### Author:  [@jamblejoe](https://discourse.julialang.org/u/jamblejoe)
#### Post date: [March 19, 2021, 12:49pm UTC](https://discourse.julialang.org/t/constant-linear-equation-d-dt-x-ax-with-differentialequations-jl/57532/3 "2021-03-19T12:49:34Z")
I will open a PR shortly. I had to import `OrdinaryDiffEq` explicitly besides `DifferentialEquations`. Is this intended?
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### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [March 19, 2021, 12:56pm UTC](https://discourse.julialang.org/t/constant-linear-equation-d-dt-x-ax-with-differentialequations-jl/57532/4 "2021-03-19T12:56:12Z")
Not intended. DifferentialEquations.jl should be used in all of the docs, but this is explicitly using only an OrdinaryDiffEq solver so you can just call it directly for lower dependency counts.
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### Author:  [@jamblejoe](https://discourse.julialang.org/u/jamblejoe)
#### Post date: [March 19, 2021, 12:57pm UTC](https://discourse.julialang.org/t/constant-linear-equation-d-dt-x-ax-with-differentialequations-jl/57532/5 "2021-03-19T12:57:31Z")
Ok thanks!