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26 changes: 26 additions & 0 deletions .github/workflows/DocsPreviewCleanup.yml
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name: DocsPreviewCleanup

on:
pull_request:
types: [closed]

jobs:
cleanup:
runs-on: ubuntu-latest
steps:
- name: Checkout gh-pages branch
uses: actions/checkout@v2
with:
ref: gh-pages
- name: Delete preview and history + push changes
run: |
if [ -d "previews/PR$PRNUM" ]; then
git config user.name "Documenter.jl"
git config user.email "[email protected]"
git rm -rf "previews/PR$PRNUM"
git commit -m "delete preview"
git branch gh-pages-new $(echo "delete history" | git commit-tree HEAD^{tree})
git push --force origin gh-pages-new:gh-pages
fi
env:
PRNUM: ${{ github.event.number }}
322 changes: 3 additions & 319 deletions README.md
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# JuliaBUGS.jl
[![Stable](https://img.shields.io/badge/docs-stable-blue.svg)](https://TuringLang.github.io/JuliaBUGS.jl/stable)
[![Dev](https://img.shields.io/badge/docs-dev-blue.svg)](https://TuringLang.github.io/JuliaBUGS.jl/dev)

A modern implementation of the BUGS probabilistic programming language in Julia.

## Caution!

JuliaBUGS is still in beta and may not be ready for serious use.

## Installation
To install the package, run the following command in the Julia REPL:
```julia
] # Enter Pkg mode by pressing `] `
(@v1.9) pkg> add JuliaBUGS
```
Then run the following command to use the package:
```julia
using JuliaBUGS
```

## Example: Logistic Regression with Random Effects
We will use the [Seeds](https://chjackson.github.io/openbugsdoc/Examples/Seeds.html) model for demonstration.
This example concerns the proportion of seeds that germinated on each of 21 plates. Here, we transform the data into a `NamedTuple`:

```julia
data = (
r = [10, 23, 23, 26, 17, 5, 53, 55, 32, 46, 10, 8, 10, 8, 23, 0, 3, 22, 15, 32, 3],
n = [39, 62, 81, 51, 39, 6, 74, 72, 51, 79, 13, 16, 30, 28, 45, 4, 12, 41, 30, 51, 7],
x1 = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1],
x2 = [0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1],
N = 21,
)
```

where `r[i]` is the number of germinated seeds and `n[i]` is the total number of the seeds on the $i$-th plate.
Let $p_i$ be the probability of germination on the $i$-th plate. Then, the model is defined by:

$$
\begin{aligned}
b_i &\sim \text{Normal}(0, \tau) \\
\text{logit}(p_i) &= \alpha_0 + \alpha_1 x_{1 i} + \alpha_2 x_{2i} + \alpha_{12} x_{1i} x_{2i} + b_{i} \\
r_i &\sim \text{Binomial}(p_i, n_i)
\end{aligned}
$$

where $x_{1i}$ and $x_{2i}$ are the seed type and root extract of the $i$-th plate.
The original BUGS program for the model is:
```R
model
{
for( i in 1 : N ) {
r[i] ~ dbin(p[i],n[i])
b[i] ~ dnorm(0.0,tau)
logit(p[i]) <- alpha0 + alpha1 * x1[i] + alpha2 * x2[i] +
alpha12 * x1[i] * x2[i] + b[i]
}
alpha0 ~ dnorm(0.0, 1.0E-6)
alpha1 ~ dnorm(0.0, 1.0E-6)
alpha2 ~ dnorm(0.0, 1.0E-6)
alpha12 ~ dnorm(0.0, 1.0E-6)
tau ~ dgamma(0.001, 0.001)
sigma <- 1 / sqrt(tau)
}
```

## Modeling Language

### Writing a Model in BUGS
BUGS language syntax: [BNF definition](https://github.com/TuringLang/JuliaBUGS.jl/blob/master/archive/parser_attempts/BNF.txt)

Language References:
- [MultiBUGS](https://www.multibugs.org/documentation/latest/)
- [OpenBUGS](https://chjackson.github.io/openbugsdoc/Manuals/ModelSpecification.html)

Implementations in C++ and R:
- [JAGS](https://sourceforge.net/p/mcmc-jags/code-0/ci/default/tree/) and its [user manual](https://people.stat.sc.edu/hansont/stat740/jags_user_manual.pdf)
- [Nimble](https://r-nimble.org/)

### Writing a Model in Julia
We provide a macro solution which allows users to write down model definitions using Julia:

```julia
model_def = @bugs begin
for i in 1:N
r[i] ~ dbin(p[i], n[i])
b[i] ~ dnorm(0.0, tau)
p[i] = logistic(alpha0 + alpha1 * x1[i] + alpha2 * x2[i] + alpha12 * x1[i] * x2[i] + b[i])
end
alpha0 ~ dnorm(0.0, 1.0E-6)
alpha1 ~ dnorm(0.0, 1.0E-6)
alpha2 ~ dnorm(0.0, 1.0E-6)
alpha12 ~ dnorm(0.0, 1.0E-6)
tau ~ dgamma(0.001, 0.001)
sigma = 1 / sqrt(tau)
end
```
BUGS syntax carries over almost one-to-one to Julia, with minor exceptions.
In general, when basic Julia syntax and BUGS syntax conflict, it is necessary to use Julia syntax.
For example, curly braces are replaced with `begin ... end` blocks, and `for` loops do not require parentheses.
In addition, Julia uses `f(x) = ...` as a shorthand for function definition, so BUGS' link function syntax can be confusing and ambiguous.
Thus, instead of calling the link function, we call the inverse link function from the RHS.

### Support for Legacy BUGS Programs
The `@bugs` macro also works with original (R-like) BUGS syntax:

```julia
model_def = @bugs("""
model{
for( i in 1 : N ) {
r[i] ~ dbin(p[i],n[i])
b[i] ~ dnorm(0.0,tau)
logit(p[i]) <- alpha0 + alpha1 * x1[i] + alpha2 * x2[i] +
alpha12 * x1[i] * x2[i] + b[i]
}
alpha0 ~ dnorm(0.0,1.0E-6)
alpha1 ~ dnorm(0.0,1.0E-6)
alpha2 ~ dnorm(0.0,1.0E-6)
alpha12 ~ dnorm(0.0,1.0E-6)
tau ~ dgamma(0.001,0.001)
sigma <- 1 / sqrt(tau)
}
""", true)
```

By default, `@bugs` will translate R-style variable names like `a.b.c` to `a_b_c`, user can pass `false` as the second argument to disable this.
We still encourage users to write new programs using the Julia-native syntax, because of better debuggability and perks like syntax highlighting.

### Using Self-defined Functions and Distributions
Users can register their own functions and distributions with macros. However, note that any functions used must be _pure_ mathematical functions, i.e., side-effect free.

```julia
julia> # Should be restricted to pure functions that do simple operations
@register_primitive function f(x)
return x + 1
end

julia> JuliaBUGS.f(2)
3
```

Users can also `introduce` a function into `JuliaBUGS`, by

```julia
julia> f(x) = x + 1

julia> @register_primitive(f)

julia> JuliaBUGS.f(1)
2
```

After registering the function or distributions, they can be used just like any other functions or distributions provided by BUGS.

## Compilation

For now, the `compile` function will create a `BUGSModel`, which implements [`LogDensityProblems.jl`](https://github.com/tpapp/LogDensityProblems.jl) interface.

```julia
compile(model_def::Expr, data, initializations),
```

The function `compile` takes three arguments:
- the output of `@bugs`,
- the data, and
- the initializations of parameters.

```julia
initializations = Dict(:alpha => 1, :beta => 1)
```

then we can compile the model with the data and initializations,
```julia
model = compile(model_def, data, initializations)
```

`LogDensityProblemsAD.jl` defined some extensions that support automatic differentiation packages.
For example, with `ReverseDiff.jl`

```julia
using LogDensityProblemsAD, ReverseDiff

ad_model = ADgradient(:ReverseDiff, model; compile=Val(true))
```
Here `ad_model` will also implement all the interfaces of `LogDensityProblems.jl`.
`LogDensityProblemsAD.jl` will automatically add the interface function `logdensity_and_gradient` to the model, which will return the log density and gradient of the model.
And `ad_model` can be used in the same way as `model` in the example below.


## Inference

For a differentiable model, we can use [`AdvancedHMC.jl`](https://github.com/TuringLang/AdvancedHMC.jl) to perform inference.
For instance,

```julia
using AdvancedHMC, AbstractMCMC, LogDensityProblems, MCMCChains

n_samples, n_adapts = 2000, 1000

D = LogDensityProblems.dimension(model); initial_θ = rand(D)

samples_and_stats = AbstractMCMC.sample(
ad_model,
NUTS(0.8),
n_samples;
chain_type = Chains,
n_adapts = n_adapts,
init_params = initial_θ,
discard_initial = n_adapts
)
```

This will return the MCMC Chain,

```julia
Chains MCMC chain (2000×40×1 Array{Real, 3}):

Iterations = 1001:1:3000
Number of chains = 1
Samples per chain = 2000
parameters = alpha0, alpha12, alpha1, alpha2, tau, b[16], b[12], b[10], b[14], b[13], b[7], b[6], b[20], b[1], b[4], b[5], b[2], b[18], b[8], b[3], b[9], b[21], b[17], b[15], b[11], b[19], sigma
internals = lp, n_steps, is_accept, acceptance_rate, log_density, hamiltonian_energy, hamiltonian_energy_error, max_hamiltonian_energy_error, tree_depth, numerical_error, step_size, nom_step_size, is_adapt

Summary Statistics
parameters mean std mcse ess_bulk ess_tail rhat ess_per_sec
Symbol Float64 Float64 Float64 Real Float64 Float64 Missing

alpha0 -0.5642 0.2320 0.0084 766.9305 1022.5211 1.0021 missing
alpha12 -0.8489 0.5247 0.0170 946.0418 1044.1109 1.0002 missing
alpha1 0.0587 0.3715 0.0119 966.4367 1233.2257 1.0007 missing
alpha2 1.3852 0.3410 0.0127 712.2978 974.1566 1.0002 missing
tau 1.8880 0.7705 0.0447 348.9331 338.3655 1.0030 missing
b[16] -0.2445 0.4459 0.0132 1528.0578 843.8225 1.0003 missing
b[12] 0.2050 0.3602 0.0086 1868.6126 1202.1363 0.9996 missing
b[10] -0.3500 0.2893 0.0090 1047.3119 1245.9358 1.0008 missing
⋮ ⋮ ⋮ ⋮ ⋮ ⋮ ⋮ ⋮
19 rows omitted

Quantiles
parameters 2.5% 25.0% 50.0% 75.0% 97.5%
Symbol Float64 Float64 Float64 Float64 Float64

alpha0 -1.0143 -0.7143 -0.5590 -0.4100 -0.1185
alpha12 -1.9063 -1.1812 -0.8296 -0.5153 0.1521
alpha1 -0.6550 -0.1822 0.0512 0.2885 0.8180
alpha2 0.7214 1.1663 1.3782 1.5998 2.0986
tau 0.5461 1.3941 1.8353 2.3115 3.6225
b[16] -1.2359 -0.4836 -0.1909 0.0345 0.5070
b[12] -0.4493 -0.0370 0.1910 0.4375 0.9828
b[10] -0.9570 -0.5264 -0.3331 -0.1514 0.1613
⋮ ⋮ ⋮ ⋮ ⋮ ⋮
19 rows omitted

```

This is consistent with the result in the [OpenBUGS seeds example](https://chjackson.github.io/openbugsdoc/Examples/Seeds.html).

## Parallel and Distributed Sampling with `AbstractMCMC`
`AbstractMCMC` and `AdvancedHMC` support both parallel and distributed sampling.

### Parallel Sampling
To perform multi-threaded sampling of multiple chains, start the Julia session with the `-t <n_threads>` argument.
The model compilation code remains the same, and we can sample multiple chains in parallel as follows:

```julia
n_chains = 4
samples_and_stats = AbstractMCMC.sample(
ad_model,
AdvancedHMC.NUTS(0.65),
AbstractMCMC.MCMCThreads(),
n_samples,
n_chains;
chain_type = Chains,
n_adapts = n_adapts,
init_params = [initial_θ for _ = 1:n_chains],
discard_initial = n_adapts,
)
```

In this case, we pass two additional arguments to `AbstractMCMC.sample`:
- `AbstractMCMC.MCMCThreads()`: the sampler type, and
- `n_chains`: the number of chains to sample.

### Distributed Sampling
To perform distributed sampling of multiple chains, start the Julia session with the `-p <n_processes>` argument.

In distributed mode, ensure that all functions and modules are available on all processes.
Use `@everywhere` to make the functions and modules available on all processes.

For example:

```julia
@everywhere begin
using JuliaBUGS, LogDensityProblems, LogDensityProblemsAD, AbstractMCMC, AdvancedHMC, MCMCChains, ReverseDiff # also other packages one may need

# Define the functions to use
# Use `@register_primitive` to register the functions to use in the model

# Distributed can handle data dependencies in some cases, for more detail, see https://docs.julialang.org/en/v1/manual/distributed-computing/

end

n_chains = nprocs() - 1 # use all the processes except the master process
samples_and_stats = AbstractMCMC.sample(
ad_model,
AdvancedHMC.NUTS(0.65),
AbstractMCMC.MCMCDistributed(),
n_samples,
n_chains;
chain_type = Chains,
n_adapts = n_adapts,
init_params = [initial_θ for _ = 1:n_chains], # each chain has its own initial parameters
discard_initial = n_adapts,
progress = false, # Base.TTY creating problems in distributed setting
)
```

In this case, we pass two additional arguments to `AbstractMCMC.sample`:
- `AbstractMCMC.MCMCDistributed()`: the sampler type, and
- `n_chains`: the number of chains to sample.
Note that the `init_params` argument is now a vector of initial parameters for each chain.
Sometimes the progress logger can cause problems in distributed setting, so we can disable it by setting `progress = false`.

## More Examples
We have transcribed all the examples from the first volume of the BUGS Examples ([original](https://www.multibugs.org/examples/latest/VolumeI.html) and [transcribed](https://github.com/TuringLang/JuliaBUGS.jl/tree/master/src/BUGSExamples/Volume_I)). All programs and data are included, and can be compiled using the steps described in the tutorial above.
For a working example, you can follow this [link](https://turinglang.org/JuliaBUGS.jl/dev/example).
4 changes: 3 additions & 1 deletion docs/make.jl
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Expand Up @@ -9,10 +9,12 @@ makedocs(;
sitename="JuliaBUGS.jl",
pages=[
"Introduction" => "index.md",
"Example" => "example.md",
"API" => [
"General" => "api.md",
"Functions" => "functions.md",
"Distributions" => "distributions.md",
"User-defined Functions and Distributions" => "user_defined_functions.md",
],
"Plotting" => "graph_plotting.md",
"R Interface" => "R_interface.md",
Expand All @@ -22,4 +24,4 @@ makedocs(;
],
)

deploydocs(; repo="github.com/TuringLang/JuliaBUGS.jl.git")
deploydocs(; repo="github.com/TuringLang/JuliaBUGS.jl.git", push_preview=true)
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