# MCMC of mixture model using Mamba
**URL:** https://discourse.julialang.org/t/mcmc-of-mixture-model-using-mamba/31125
**Category:** General Usage
**Tags:** question
**Created:** [November 15, 2019, 11:35am UTC](https://discourse.julialang.org/t/mcmc-of-mixture-model-using-mamba/31125 "2019-11-15T11:35:01Z")
**Posts on this page:** 9
**Page:** 1
### Author:  [@SSU](https://discourse.julialang.org/u/SSU)
#### Post date: [November 15, 2019, 11:35am UTC](https://discourse.julialang.org/t/mcmc-of-mixture-model-using-mamba/31125/1 "2019-11-15T11:35:01Z")
I am trying to fit my experimental data( ~40k circular data, [-\pi, +\pi], bimodal) with mixture of [von mises distribution](https://juliastats.org/Distributions.jl/stable/univariate/#Distributions.VonMises) using [Mamba](https://mambajl.readthedocs.io/en/latest/).
I want to predict the parameters(\mu, \kappa, weights) of the data.
# Problem
The following code returns
`TypeError: in new, expected ScalarStochastic, got Float64`
However, I can’t figure out what is wrong with my code…
How can I fix this error?
Any suggestions are welcomed !!
Thank you in advance.
# Dependencies and data
```Julia
# Julia version 1.2.0
using Mamba # v0.12.2
using Distributions # v0.21.8
data = Dict{Symbol, Any}(
:sample => Array(data[:, 1]),
:N => length(data[:, 1]),
)
"""
Dict{Symbol,Any} with 2 entries:
:N => 374718
:sample => [2.49329, 0.143419, -1.23308, 2.42615, -1.74222, -0.180238, 0.3280…
"""
```
# Model specification
\kappa1 \sim Gamma(\alpha=1., \beta=1.0)\\ \kappa2 \sim Gamma(\alpha=1., \beta=1.0)\\ \mu1 \sim VonMises(\mu=0, \kappa=0.5)\\ \mu2 \sim VonMises(\mu=pi, \kappa=0.5)\\ w \sim Dirichlet([1., 1.])\\ y \sim w[1]\*VonMises(\mu=\mu1, \kappa=\kappa1) + w[2]\*VonMises(\mu=\mu2, \kappa=\kappa2)
```Julia
model = Model(
kappa1 = Stochastic(
() -> Gamma(),
),
kappa2 = Stochastic(
() -> Gamma(),
),
mu1 = Stochastic(
() -> VonMises(0, 0.5),
),
mu2 = Stochastic(
() -> VonMises(pi, 0.5),
),
w = Stochastic(1,
() -> Dirichlet(ones(2))
),
y = Stochastic(1,
(mu1, mu2, kappa1, kappa2, w) ->
MixtureModel(VonMises[VonMises(mu1, kappa1), VonMises(mu2, kappa2)], w),
false),
)
scheme = [NUTS([:kappa1, :kappa2, :mu1, :mu2, :w])]
setsamplers!(model, scheme)
```
# Initial values and sampling
```Julia
inits = [
Dict{Symbol, Any}(
:y => data[:sample],
:kappa1 => rand(Gamma(1, 1)),
:kappa2 => rand(Gamma(1, 1)),
:mu1 => rand(VonMises(0, 0.5)),
:mu2 => rand(VonMises(0, 0.5)),
:w => [0.5, 0.5]
)
]
## MCMC(NUTS)
nuts_inference = mcmc(model, data, inits, 5000, burnin=1000, thin=2, chains=1)
```
returns
```Julia
TypeError: in new, expected ScalarStochastic, got Float64
```
---
### Author:  [@Vasily\_Pisarev](https://discourse.julialang.org/u/Vasily_Pisarev)
#### Post date: [November 15, 2019, 8:58pm UTC](https://discourse.julialang.org/t/mcmc-of-mixture-model-using-mamba/31125/2 "2019-11-15T20:58:14Z")
The error means that one of the type constructor got an object of unexpected datatype as parameter.
To get more help from here, you have to post the full call stack after the error message.
Usually, the function at the top of the call stack is the one in which the error happened, and there you have the source file and line where it happened.
---
### Author:  [@SSU](https://discourse.julialang.org/u/SSU)
#### Post date: [November 16, 2019, 8:50am UTC](https://discourse.julialang.org/t/mcmc-of-mixture-model-using-mamba/31125/3 "2019-11-16T08:50:14Z")
Thank you for your reply.
The followings are the full stack.
There seems to be many mistakes in my code, but still, I don’t understand the TypeError in the top.
I’m giving vonmises distribution a ScalarStochastic(\mu1, \mu2, \kappa1 ,\kappa2) as a argument, not a Float64.
Am I making some kind of radical misunderstaning?
```julia
TypeError: in new, expected ScalarStochastic, got Float64
Stacktrace:
[1] Type at C:\Users\username\.julia\packages\Distributions\OdJGZ\src\univariate\continuous\vonmises.jl:22 [inlined]
[2] #VonMises#105 at C:\Users\username\.julia\packages\Distributions\OdJGZ\src\univariate\continuous\vonmises.jl:29 [inlined]
[3] Type at C:\Users\username\.julia\packages\Distributions\OdJGZ\src\univariate\continuous\vonmises.jl:28 [inlined]
[4] (::getfield(Main, Symbol("##164#170")))(::ScalarStochastic, ::ScalarStochastic, ::ScalarStochastic, ::ScalarStochastic, ::ArrayStochastic{1}) at .\In[20]:21
[5] (::getfield(Main, Symbol("##181#182")))(::Model) at .\array.jl:0
[6] setinits!(::ArrayStochastic{1}, ::Model, ::Array{Float64,1}) at C:\Users\username\.julia\packages\Mamba\Jotzr\src\model\dependent.jl:173
[7] setinits!(::Model, ::Dict{Symbol,Any}) at C:\Users\username\.julia\packages\Mamba\Jotzr\src\model\initialization.jl:11
[8] setinits!(::Model, ::Array{Dict{Symbol,Any},1}) at C:\Users\username\.julia\packages\Mamba\Jotzr\src\model\initialization.jl:24
[9] #mcmc#23(::Int64, ::Int64, ::Int64, ::Bool, ::typeof(mcmc), ::Model, ::Dict{Symbol,Any}, ::Array{Dict{Symbol,Any},1}, ::Int64) at C:\Users\username\.julia\packages\Mamba\Jotzr\src\model\mcmc.jl:30
[10] (::getfield(Mamba, Symbol("#kw##mcmc")))(::NamedTuple{(:burnin, :thin, :chains),Tuple{Int64,Int64,Int64}}, ::typeof(mcmc), ::Model, ::Dict{Symbol,Any}, ::Array{Dict{Symbol,Any},1}, ::Int64) at .\none:0
[11] top-level scope at In[22]:1
```
---
### Author:  [@Vasily\_Pisarev](https://discourse.julialang.org/u/Vasily_Pisarev)
#### Post date: [November 16, 2019, 5:41pm UTC](https://discourse.julialang.org/t/mcmc-of-mixture-model-using-mamba/31125/4 "2019-11-16T17:41:33Z")
Looks like some of your Von Mises constructors are called with the first argument being a `ScalarStochastic` and the second being a `Float64`, while the actual constructor expects the argument types to be the same.
The code that triggers the error is in the 21st line of your 20th Jupyter cell, which is impossible to decipher without the actual notebook.
Btw, it’s best to leave `[VonMises(mu1, kappa1), VonMises(mu2, kappa2)]` as it is or use `VonMises{typeof(mu1)}[VonMises(mu1, kappa1), VonMises(mu2, kappa2)]` to avoid an array with an abstract element type.
---
### Author:  [@SSU](https://discourse.julialang.org/u/SSU)
#### Post date: [November 17, 2019, 7:20am UTC](https://discourse.julialang.org/t/mcmc-of-mixture-model-using-mamba/31125/5 "2019-11-17T07:20:47Z")
Thank you for your advice.
I changed my code.
21st line of my 20th cell was indicating this part.
```nohighlight
20 y = Stochastic(1,
21 (mu1, mu2, kappa1, kappa2, w) ->
22 MixtureModel([VonMises(mu1, kappa1), VonMises(mu2, kappa2)], w),
23 false),
```
I’m pretty sure that all of these arguments are `ScalarStochastic` because the codes below returns no error.
Giving two `ScalarStochastic` parameters per one von mises distribution will cause same TypeError.
This might be a bug.
```nohighlight
# No error
y = Stochastic(1,
(mu1, mu2, w) ->
MixtureModel([VonMises(mu1, 1), VonMises(mu2, 1)], w),
false),
```
```nohighlight
# No error
y = Stochastic(1,
(kappa1, kappa2, w) ->
MixtureModel([VonMises(0, kappa1), VonMises(0, kappa2)], w),
false),
```
---
### Author:  [@SSU](https://discourse.julialang.org/u/SSU)
#### Post date: [November 30, 2019, 2:01pm UTC](https://discourse.julialang.org/t/mcmc-of-mixture-model-using-mamba/31125/6 "2019-11-30T14:01:50Z")
I’m still stuck here.
Does anyone know the solution?
---
### Author:  [@Christopher\_Fisher](https://discourse.julialang.org/u/Christopher_Fisher)
#### Post date: [November 30, 2019, 6:07pm UTC](https://discourse.julialang.org/t/mcmc-of-mixture-model-using-mamba/31125/7 "2019-11-30T18:07:57Z")
Would Turing or DynamicHMC work for your problem? In my experience, those packages have more thorough documentation and have more active communities.
---
### Author:  [@bdeonovic](https://discourse.julialang.org/u/bdeonovic)
#### Post date: [December 2, 2019, 4:54pm UTC](https://discourse.julialang.org/t/mcmc-of-mixture-model-using-mamba/31125/8 "2019-12-02T16:54:10Z")
Sorry for the late response. This appears to be a problem with Distributions package (the VonMises distribution) and parameter checking. I will look into it today and file a pull request if I can fix it.
---
### Author:  [@SSU](https://discourse.julialang.org/u/SSU)
#### Post date: [December 7, 2019, 10:47am UTC](https://discourse.julialang.org/t/mcmc-of-mixture-model-using-mamba/31125/9 "2019-12-07T10:47:15Z")
Thank you so much for your reply!
I will try other packages.