# Parameters of IDA DAE solver
**URL:** https://discourse.julialang.org/t/parameters-of-ida-dae-solver/61366
**Category:** Modelling & Simulations
**Tags:** question
**Created:** [May 18, 2021, 2:45pm UTC](https://discourse.julialang.org/t/parameters-of-ida-dae-solver/61366 "2021-05-18T14:45:32Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [May 18, 2021, 2:45pm UTC](https://discourse.julialang.org/t/parameters-of-ida-dae-solver/61366/1 "2021-05-18T14:45:32Z")
I have the following code:
```julia
using DifferentialEquations, Sundials, StaticArrays
using Revise
if ! @isdefined KPS3
includet("../src/KPS3.jl")
using .KPS3
end
my_state = KPS3.get_state()
clear(my_state)
y0, yd0 = KPS3.init(my_state)
tspan = (0.0, 0.05) # time span; fails when changed to (0.0, 0.06)
differential_vars = ones(Bool, 36)
prob = DAEProblem(residual!, yd0, y0, tspan, differential_vars=differential_vars)
sol = solve(prob, IDA(), saveat=0.001, abstol=0.01, reltol=0.001)
time = sol.t
println(sol.retcode)
pos_x = sol[3*5+1, :]
pos_z = sol[3*5+3, :]
```
It works fine. You can check it out here: [https://github.com/ufechner7/KiteViewer/tree/sim](https://github.com/ufechner7/KiteViewer/tree/sim)
(careful, use branch sim)
But if I increase the simulation time to 0.06 seconds it fails with the following error
message:
```julia
julia> include("src/RTSim.jl")
[IDAS ERROR] IDASolve
At t = 0.0599924 and h = 2.40789e-162, the corrector convergence failed repeatedly or with |h| = hmin.
3.462572 seconds (10.40 M allocations: 599.441 MiB, 15.08% gc time)
ConvergenceFailure
```
I would like to set the following parameters of the solver to make it work:
```julia
inith = 0.002
maxord = 3
pos_tol = 2.0/ 100.0
vel_tol = pos_tol / 60.0
atol = vel_tol * ones(36)
for i in 1:18
atol[i] = pos_tol
end
rtol = 1e-3
```
The names I am using here are coming from the Python/ Assimulo code that I am converting to Julia,
so I might have to use slightly different names. (See: [IDA — Assimulo 3.0 documentation](https://jmodelica.org/assimulo/DAE_IDA.html))
Special question: Can I use arrays for the absolute end the relative tolerance?
Any ideas how to set inith, maxord, rtol and atol when using IDA from DifferentialEquations?
Uwe
---
### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [May 18, 2021, 4:33pm UTC](https://discourse.julialang.org/t/parameters-of-ida-dae-solver/61366/2 "2021-05-18T16:33:47Z")
I created an issue: [Document IDA options · Issue #306 · SciML/Sundials.jl · GitHub](https://github.com/SciML/Sundials.jl/issues/306)
---
### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [May 18, 2021, 4:54pm UTC](https://discourse.julialang.org/t/parameters-of-ida-dae-solver/61366/3 "2021-05-18T16:54:47Z")
OK, I found the functions:
function IDASVtolerances(ida\_mem, reltol::realtype, abstol::N\_Vector)
function IDASetMaxOrd(ida\_mem, maxord::Cint)
function IDASetInitStep(ida\_mem, hin::realtype)
In the file:
[https://github.com/SciML/Sundials.jl/blob/master/src/API/idas.jl](https://github.com/SciML/Sundials.jl/blob/master/src/API/idas.jl)
But how can I use them?
Where do I get ida\_mem from?
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [May 18, 2021, 5:39pm UTC](https://discourse.julialang.org/t/parameters-of-ida-dae-solver/61366/4 "2021-05-18T17:39:41Z")
> [@ufechner7](#):
>
> Any ideas how to set inith, maxord, rtol and atol when using IDA from DifferentialEquations?
Most of those are common arguments documented in the same place they always are:
[https://diffeq.sciml.ai/stable/basics/common\_solver\_opts/](https://diffeq.sciml.ai/stable/basics/common_solver_opts/)
The order though is specific to IDA, so it’s documented in the same place all of the algorithm-specific arguments are, i.e. in the algorithm’s documentation.
[https://diffeq.sciml.ai/stable/solvers/dae\_solve/#Sundials.jl](https://diffeq.sciml.ai/stable/solvers/dae_solve/#Sundials.jl)
It all follows a pattern.
---
### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [May 18, 2021, 6:42pm UTC](https://discourse.julialang.org/t/parameters-of-ida-dae-solver/61366/5 "2021-05-18T18:42:42Z")
Ok, but how can I specify a vector for abstol?
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [May 18, 2021, 6:43pm UTC](https://discourse.julialang.org/t/parameters-of-ida-dae-solver/61366/6 "2021-05-18T18:43:13Z")
Just make it a vector. `solve(prob,alg,abstol=[1e-3,1e-4])`
> The scaled error is guaranteed to be `<1` for a given local error estimate (note: error estimates are local unless the method specifies otherwise). `abstol` controls the non-scaling error and thus can be though of as the error around zero. `reltol` scales with the size of the dependent variables and so one can interpret `reltol=1e-3` as roughly being (locally) correct to 3 digits. Note tolerances can be specified element-wise by passing a vector whose size matches `u0` .
---
### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [May 18, 2021, 6:43pm UTC](https://discourse.julialang.org/t/parameters-of-ida-dae-solver/61366/7 "2021-05-18T18:43:53Z")
OK, lets see if that works.
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [May 18, 2021, 6:45pm UTC](https://discourse.julialang.org/t/parameters-of-ida-dae-solver/61366/8 "2021-05-18T18:45:05Z")
It should, for reference the source code shows how the common interface lowers to using the functions you’re talking about:
>