# Help with deSolveDiffEq
**URL:** https://discourse.julialang.org/t/help-with-desolvediffeq/47497
**Category:** New to Julia
**Tags:** ode
**Created:** [September 29, 2020, 4:48pm UTC](https://discourse.julialang.org/t/help-with-desolvediffeq/47497 "2020-09-29T16:48:48Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@HerAdri](https://discourse.julialang.org/u/HerAdri)
#### Post date: [September 29, 2020, 4:48pm UTC](https://discourse.julialang.org/t/help-with-desolvediffeq/47497/1 "2020-09-29T16:48:48Z")
Why with deSolveDiffEq I am not receiving all the solutions of the system, as can be seen in the examples?
I only get these results
```julia
19:42:41->>retcode: Default
Interpolation: 1st order linear
t: 2-element view(::Array{Float64,2}, :, 1) with eltype Float64:
0.0
50.0
u: 2-element Array{Array{Float64,1},1}:
[0.0, 0.66]
[-33.0, 15.510000000000002]
### Examples
using DifferentialEquations
using Plots; gr()
function integrate_ODE!(du,u,t)
du[1] = -0.4*u[1] - u[2]
du[2] = u[1] + 0.45*u[2]
end
u0 = [0.0,0.66]
tspan = (0.0,50.0)
prob = ODEProblem(integrate_ODE!,u0,tspan)
sol = solve(prob)# Euler ImplicitEuler
plot(sol,linewidth=2,xaxis="t",layout=(2,1))
plot(sol,vars=(1,2), lw=1)
#
using OrdinaryDiffEq
prob = ODEProblem(integrate_ODE!,u0,tspan)
OrdinaryDiffEq.solve(prob, ImplicitEuler())
plot(sol,linewidth=2,xaxis="t",layout=(2,1))
plot(sol,vars=(1,2), lw=1)
#
A=[-0.4 -1.0
1.0 0.45]
u0 = [0.0; 0.66]
tspan = (0.0,50.0)
f(u,p,t)=A*u
prob = ODEProblem(f,u0,tspan)
sol=solve(prob)
plot(sol,linewidth=2,xaxis="t",layout=(2,1))
plot(sol,vars=(1,2), lw=1)
#
using deSolveDiffEq
u0 = [0.0;0.66]
tspan = (0.0,50.0)
prob = ODEProblem(integrate_ODE!,u0,tspan)
sol = solve(prob,deSolveDiffEq.euler())
#
```
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [September 30, 2020, 1:59am UTC](https://discourse.julialang.org/t/help-with-desolvediffeq/47497/2 "2020-09-30T01:59:36Z")
> [@HerAdri](#):
>
> `integrate_ODE!(du,u,t)`
you mean `integrate_ODE!(du,u,p,t)`?
---
### Author:  [@HerAdri](https://discourse.julialang.org/u/HerAdri)
#### Post date: [September 30, 2020, 5:43am UTC](https://discourse.julialang.org/t/help-with-desolvediffeq/47497/3 "2020-09-30T05:43:24Z")
In function integr\_ODE! (du, u, t), I do not declare parameters. Should I in the declaration of the function, enter it, even though in the body of the function I don’t use them?
```julia
function integrate_ODE!(du,u,t)
du[1] = -0.4*u[1] - u[2]
du[2] = u[1] + 0.45*u[2]
end
```
---
### Author:  [@HerAdri](https://discourse.julialang.org/u/HerAdri)
#### Post date: [September 30, 2020, 5:58am UTC](https://discourse.julialang.org/t/help-with-desolvediffeq/47497/4 "2020-09-30T05:58:08Z")
```julia-auto
function integrate_ODE!(du,u,p,t)
du[1] = -0.4*u[1] - u[2]
du[2] = u[1] + 0.45*u[2]
end
using deSolveDiffEq
u0 = [0.0;0.66]
tspan = (0.0,50.0)
prob = ODEProblem(integrate_ODE!,u0,tspan)
sol = solve(prob,deSolveDiffEq.euler())
08:51:07->>retcode: Default
Interpolation: 1st order linear
t: 2-element view(::Array{Float64,2}, :, 1) with eltype Float64:
0.0
50.0
u: 2-element Array{Array{Float64,1},1}:
[0.0, 0.66]
[-33.0, 15.510000000000002]
```
####
Introducing in solve, saveat = 0.1, I get the results!
```julia-auto
sol = solve(prob,deSolveDiffEq.euler(),saveat=0.1)
>retcode: Default
Interpolation: 1st order linear
t: 501-element view(::Array{Float64,2}, :, 1) with eltype Float64:
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
⋮
49.1
49.2
49.3
49.4
49.5
49.6
49.7
49.8
49.9
50.0
u: 501-element Array{Array{Float64,1},1}:
[0.0, 0.66]
[-0.066, 0.6897]
[-0.13233, 0.7141365]
[-0.19845045, 0.7330396425]
[-0.26381639625000003, 0.7461813814125]
[-0.32788187854125, 0.7533779039510625]
[-0.39010439379470624, 0.7544917217747353]
[-0.4499493902203915, 0.7494334098751279]
[-0.5068947555990887, 0.7381629742974695]
[-0.5604352628048721, 0.7206908325809467]
[-0.6100869355507719, 0.6970783937666021]
⋮
[-4.192619673242593, 17.848340068051428]
[-5.809748893118055, 18.23225340378949]
[-7.400584277772191, 18.471729917648197]
[-8.951733898426145, 18.56289933616515]
[-10.449954476105635, 18.503056416449965]
[-11.882261938706426, 18.29069850757965]
[-13.236041311916154, 17.925553746550086]
[-14.499155034094445, 17.408599533953254]
[-15.660048786126008, 16.742071009571696]
[-16.707853935638152, 15.929459326389809]
```
My next question,
How to see the saveat, which was used by default in the previous examples? To be able to replicate it in this case
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [September 30, 2020, 1:32pm UTC](https://discourse.julialang.org/t/help-with-desolvediffeq/47497/5 "2020-09-30T13:32:31Z")
> [@HerAdri](#):
>
> Introducing in solve, saveat = 0.1, I get the results!
>
> ```julia
>
> ```
> [@HerAdri](#):
>
> How to see the saveat, which was used by default in the previous examples? To be able to replicate it in this case
I think when you choose a method with fixed time steps, `deSolve` chooses to set the time step to the maximal value unless you specify a `dt` which we do implicitly through `saveat` because of how it mixes those ideas. You can’t make `deSolveDiffEq.euler` adaptive because their implementation of it is not adaptive.
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [September 30, 2020, 1:33pm UTC](https://discourse.julialang.org/t/help-with-desolvediffeq/47497/6 "2020-09-30T13:33:25Z")
BTW, I’m curious what the purpose of this exercise is. Using Euler from deSolve is a very curious thing 😆