But trying to infer the variance

```
@model [ default_factorisation = MeanField() ] function linear_regression(n,m)
a ~ MvNormalMeanCovariance(zeros(m), diagm(ones(m)))
b ~ NormalMeanVariance(0.0,1.0)
σ ~ GammaShapeRate(1.0, 1.0)
c ~ ones(n)*b
x = datavar(Matrix{Float64})
y = datavar(Vector{Float64})
z ~ x*a+c
y ~ MvNormalMeanCovariance(z ,σ .* diagm(ones(n)))
return a, y
end
results = inference(
model = Model(linear_regression, n,m),
data = (y = randn(n), x = randn(n,m)),
returnvars = (a = KeepLast(),),
iterations = 20
);
```

I get

```
ERROR: MethodError: no method matching make_node(::Type{MvNormalMeanCovariance}, ::FactorNodeCreationOptions{MeanField, Nothing, Nothing}, ::AutoVar, ::RandomVariable, ::Matrix{RandomVariable})
Closest candidates are:
make_node(::FactorGraphModel, ::FactorNodeCreationOptions, ::Any, ::Any...) at C:\Users\arn203\.julia\packages\ReactiveMP\PPQkO\src\model.jl:428
make_node(::Type{<:NormalMixture{N}}, ::F, ::M, ::P) where {N, F, M, P} at C:\Users\arn203\.julia\packages\ReactiveMP\PPQkO\src\nodes\normal_mixture.jl:266
make_node(::Type{<:GammaMixture{N}}, ::F, ::M, ::P) where {N, F, M, P} at C:\Users\arn203\.julia\packages\ReactiveMP\PPQkO\src\nodes\gamma_mixture.jl:208
...
Stacktrace:
[1] make_node(::FactorGraphModel, ::FactorNodeCreationOptions{Nothing, Nothing, Nothing}, ::Type, ::AutoVar, ::RandomVariable, ::Matrix{RandomVariable})
@ ReactiveMP C:\Users\arn203\.julia\packages\ReactiveMP\PPQkO\src\model.jl:429
[2] macro expansion
@ .\REPL[736]:11 [inlined]
[3] macro expansion
@ C:\Users\arn203\.julia\packages\GraphPPL\cjw4Q\src\model.jl:390 [inlined]
[4] create_model(::Type{linear_regression}, linear_regressionconstraints_in#4290::Nothing, linear_regressionmeta_in#4292::Nothing, linear_regressionoptions_in#4294::NamedTuple{(), Tuple{}}, n::Int64, m::Int64)
@ Main C:\Users\arn203\.julia\packages\GraphPPL\cjw4Q\src\backends\reactivemp.jl:73
[5] create_model
@ C:\Users\arn203\.julia\packages\ReactiveMP\PPQkO\src\model.jl:48 [inlined]
[6] inference(; model::ReactiveMP.ModelGenerator{linear_regression, Tuple{Int64, Int64}, Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}}, Nothing, Nothing, Nothing}, data::NamedTuple{(:y, :x), Tuple{Vector{Float64}, Matrix{Float64}}}, initmarginals::Nothing, initmessages::Nothing, constraints::Nothing, meta::Nothing, options::NamedTuple{(), Tuple{}}, returnvars::NamedTuple{(:a,), Tuple{KeepLast}}, iterations::Int64, free_energy::Bool, free_energy_diagnostics::Tuple{BetheFreeEnergyCheckNaNs, BetheFreeEnergyCheckInfs}, showprogress::Bool, callbacks::Nothing, warn::Bool)
@ ReactiveMP C:\Users\arn203\.julia\packages\ReactiveMP\PPQkO\src\inference.jl:319
[7] top-level scope
@ REPL[737]:1
```