# Set maxiters on OrdinaryDiffEq

**URL:** <https://discourse.julialang.org/t/set-maxiters-on-ordinarydiffeq/40850>\
**Category:** New to Julia\
**Tags:** question\
**Created:** [June 6, 2020, 6:40am UTC](https://discourse.julialang.org/t/set-maxiters-on-ordinarydiffeq/40850 "2020-06-06T06:40:08Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![Luigi\_Marongiu](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/luigi_marongiu/32/7909_2.png) [@Luigi\_Marongiu](https://discourse.julialang.org/u/Luigi_Marongiu)\
**Post date:** [June 6, 2020, 6:40am UTC](https://discourse.julialang.org/t/set-maxiters-on-ordinarydiffeq/40850/1 "2020-06-06T06:40:08Z")

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Hello,  
I wrote a differential equation set as follows:

```julia
function seir!(du, u, p, t)
    trans_rate, infect_rate, recovery_rate = p
    λ = trans_rate * u[3] # force of infection βI
    κ1 = λ * u[1] # λS
    κ2 = infect_rate * u[2] # fE
    κ3 = recovery_rate * u[3] # rI
    #=
    du[1] = susceptible (s)
    du[2] = exposed (i)
    du[3] = infected (r)
    du[4] = recovered (d)
    =#
    du[1] = u[1] - κ1
    du[2] = u[2] + κ1 - κ2
    du[3] = u[3] + κ2 - κ3
    du[4] = u[4] + κ3
end
# set parameters
β = 0.00001 # transmission rate
f = 0.5 # incibation time
r = 0.5 # illness time
N = 100000.0 # total population
s0 = N - 1 # initial population susceptible
e0 = 1 # initial population infected
i0 = 0 # initial population recovered
r0 = 0 # initial population deceased
tmax = 200 # time span 0-tmax
# set solver
u0 = [s0, e0, i0, r0] # initial population
p = [β, k, r, N] # parameters
tspan = (0.0, tmax) # time span
prob = ODEProblem(seir!, u0, tspan, p)
soln = solve(prob, Tsit5())

```

But when I launched it I got en error after the 20th cycle:

```julia
Warning: Interrupted. Larger maxiters is needed.
└ @ DiffEqBase ~/.julia/packages/DiffEqBase/KnYSY/src/integrator_interface.jl:329

```

How can I manage `maxiters`?  
Besides, since I could run similar equations with parameters in the order of 10^6 instead of 10^5, I think that must be something funny in the numbers: maybe the way they are formatted could affect `solve`? Should I remove the `u[j]` elements?

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<div class="post-metadata">

**Author:** ![ChrisRackauckas](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chrisrackauckas/32/77_2.png) [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)\
**Post date:** [June 6, 2020, 6:45am UTC](https://discourse.julialang.org/t/set-maxiters-on-ordinarydiffeq/40850/2 "2020-06-06T06:45:22Z")

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`soln = solve(prob, Tsit5(), maxiters=Int(1e6))`

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<div class="post-metadata">

**Author:** ![Luigi\_Marongiu](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/luigi_marongiu/32/7909_2.png) [@Luigi\_Marongiu](https://discourse.julialang.org/u/Luigi_Marongiu)\
**Post date:** [June 6, 2020, 8:33am UTC](https://discourse.julialang.org/t/set-maxiters-on-ordinarydiffeq/40850/3 "2020-06-06T08:33:14Z")

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> [@ChrisRackauckas](#):
>
> , maxiters=Int(1e6)

Thank you, it was accepted. But even with Int1e7, there is still a need for higher maxiters, which is weird because I sorted other functions without the need to change maxiters. At 10^9, it tucked the computer.  
It turned out I should remove the u[j] from the function. In that case, no maxiters is required.

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<div class="post-metadata">

**Author:** ![ChrisRackauckas](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chrisrackauckas/32/77_2.png) [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)\
**Post date:** [June 6, 2020, 3:04pm UTC](https://discourse.julialang.org/t/set-maxiters-on-ordinarydiffeq/40850/4 "2020-06-06T15:04:56Z")

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then don’t use an explicit Runge-Kutta method. This is a clear sign of stiffness.

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<div class="post-metadata">

**Author:** ![Luigi\_Marongiu](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/luigi_marongiu/32/7909_2.png) [@Luigi\_Marongiu](https://discourse.julialang.org/u/Luigi_Marongiu)\
**Post date:** [June 7, 2020, 6:30am UTC](https://discourse.julialang.org/t/set-maxiters-on-ordinarydiffeq/40850/5 "2020-06-07T06:30:45Z")

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could you please explain? I am no matematician, so these are all exotic terms to me. What should be the best algorithm and I would I choose it? Thank you

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<div class="post-metadata">

**Author:** ![ChrisRackauckas](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chrisrackauckas/32/77_2.png) [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)\
**Post date:** [June 7, 2020, 12:59pm UTC](https://discourse.julialang.org/t/set-maxiters-on-ordinarydiffeq/40850/6 "2020-06-07T12:59:12Z")

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[https://tutorials.sciml.ai/html/introduction/02-choosing\_algs.html](https://tutorials.sciml.ai/html/introduction/02-choosing_algs.html)