# StochasticDiffEq with Acausal modeling
**URL:** https://discourse.julialang.org/t/stochasticdiffeq-with-acausal-modeling/121998
**Category:** Modelling & Simulations
**Created:** [October 30, 2024, 3:30pm UTC](https://discourse.julialang.org/t/stochasticdiffeq-with-acausal-modeling/121998 "2024-10-30T15:30:25Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@Sushrut\_Deshpande](https://discourse.julialang.org/u/Sushrut_Deshpande)
#### Post date: [October 30, 2024, 3:30pm UTC](https://discourse.julialang.org/t/stochasticdiffeq-with-acausal-modeling/121998/1 "2024-10-30T15:30:25Z")
Hello,
I am trying to have a `SDESystem` instead of `ODESystem` for my acausal framework.
The following block of code fails:
```julia
using ModelingToolkit, Plots, DifferentialEquations, StochasticDiffEq
using ModelingToolkit: t_nounits as t, D_nounits as D
@connector function myconnect(;name)
vars = @variables begin
x(t), [input = true]
y(t), [input = true]
z(t), [input = true]
end
noiseeqs = [
]
SDESystem(Equation[], noiseeqs,t, vars, [];name=name)
end
function source(;name,x_,y_,z_)
@named port = myconnect()
para = @parameters begin
end
vars = @variables begin
x(t)
y(t)
z(t)
end
eqs = [
D(x) ~ 0
D(y) ~ 0
D(z) ~ 0
port.x ~ x_ # Outflow is negative
port.y ~ y_
port.z ~ z_
]
noiseeqs = [
0.1*x,
0.1*y,
0.1*z,
0,
0,
0
]
compose(SDESystem(eqs,noiseeqs ,t, vars, para;name),port)
end
function mycomp(;name)
@named _in = myconnect()
@named _out = myconnect()
para = @parameters begin
end
vars = @variables begin
x(t)
y(t)
z(t)
end
eqs = [
D(x) ~ x*cos(-t)
_out.x ~ x
D(y) ~ y*sin(-t)
_out.y ~ y
D(z) ~ Base.ifelse(t>10,z*(cos(t)),0)
_out.z ~ z
]
noiseeqs = [
0.1*x,
0,
0.1*y,
0,
0.1*z,
0
]
compose(SDESystem(eqs,noiseeqs,t, vars, para;name),_in,_out)
end
function sink(;name)
@named port = myconnect()
para = @parameters begin
end
vars = @variables begin
x(t)
y(t)
z(t)
end
eqs = [
port.x ~ x # Outflow is negative
port.y ~ y
port.z ~ z
]
noiseeqs = [
0,
0,
0
]
compose(SDESystem(eqs,noiseeqs ,t, vars, para;name),port)
end
@named src = source(x_ = 1,y_=2,z_=3)
@named comp = mycomp()
@named snk = sink()
eqs = [
connect(src.port,comp._in)
connect(comp._out,snk.port)
]
systems = [src,comp,snk]
@named model = SDESystem(eqs,t, systems=systems)
```
with the error:
```julia
ERROR: MethodError: no method matching SDESystem(::Vector{Equation}, ::Num; systems::Vector{SDESystem}, name::Symbol)
The type `SDESystem` exists, but no method is defined for this combination of argument types when trying to construct it.
```
This is my first time trying acausal system with SDE so I am sure many things are wrong here.
I am also not sure if an SDE can be made using the acausal framework.
Any guidance here would be very helpful.
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [November 3, 2024, 11:01am UTC](https://discourse.julialang.org/t/stochasticdiffeq-with-acausal-modeling/121998/2 "2024-11-03T11:01:05Z")
Using SDESystem was deprecated awhile ago for `System`. See:
> **[Modeling with Stochasticity · ModelingToolkit.jl](https://docs.sciml.ai/ModelingToolkit/stable/tutorials/stochastic_diffeq/)**
>
> Documentation for ModelingToolkit.jl.
---
### Author:  [@Sushrut\_Deshpande](https://discourse.julialang.org/u/Sushrut_Deshpande)
#### Post date: [November 3, 2024, 12:17pm UTC](https://discourse.julialang.org/t/stochasticdiffeq-with-acausal-modeling/121998/3 "2024-11-03T12:17:07Z")
Hello,
Is there a way to use it like the following? I cannot find much docs on this
The following example will not compile but I wanted to know if I can pass `@brownian` variables to the `System` the way I can pass `eqs`, `@variables`, and `@parameters`
```julia
using ModelingToolkit, StochasticDiffEq
using ModelingToolkit: t_nounits as t, D_nounits as D
using Plots
function sto(;name)
para = @parameters begin
σ=10.0
ρ=28
β=8/3
end
vars = @variables begin
x(t)
y(t)
z(t)
end
br = @brownian begin
B
end
eqs = [D(x) ~ σ * (y - x) + B,
D(y) ~ x * (ρ - z) - y ,
D(z) ~ x * y - β * z ]
System(eqs,t,vars,para,br;name)
end
@named de = sto()
sys = structural_simplify(de)
typeof(sys)
```
This example works for the `ODESystem` without using the `@brownian` variables.
---
### Author:  [@Sushrut\_Deshpande](https://discourse.julialang.org/u/Sushrut_Deshpande)
#### Post date: [November 3, 2024, 12:18pm UTC](https://discourse.julialang.org/t/stochasticdiffeq-with-acausal-modeling/121998/4 "2024-11-03T12:18:02Z")
inshort without using `@mtkbuild`
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [November 3, 2024, 1:26pm UTC](https://discourse.julialang.org/t/stochasticdiffeq-with-acausal-modeling/121998/5 "2024-11-03T13:26:00Z")
open an issue