# babette Tutorial

#### Richèl J.C. Bilderbeek

#### 2024-06-24

## Introduction

This vignette is a tutorial how to use `babette` and its most important `bbt_run_from_model` function.

First, load `babette`:

    library(babette)

The main function of `babette` is `bbt_run_from_model`. Here is part of its help:

    Do a full run: create a 'BEAST2' configuration file (like BEAUti 2),
    run 'BEAST2', parse results (like Tracer)

    Usage

    bbt_run_from_model(
      fasta_filename,
      inference_model,
      beast2_options
    )

Simplifying this to all arguments that do not have a default:

    bbt_run_from_model(
      fasta_filename
    )

## `fasta_filename`

`fasta_filename` is the argument to specify which FASTA file to work on. `babette` is bundled with some FASTA files, so obtaining a path to a FASTA file is easy:

    fasta_filename <- get_babette_path("anthus_aco_sub.fas")
    file.exists(fasta_filename)
    #> [1] TRUE

With `fasta_filename` available, we have the minimal requirements to call `bbt_run_from_model` like this:

    out <- bbt_run_from_model(fasta_filename)

Note that this code is not ran, as it would take too long. The reason this would take too long, is that the MCMC run that will be executed is set to one million states by default. To specify the MCMC options and shorten this run, the `mcmc` argument is used.

## `inference_model` and `mcmc`

The inference run’s MCMC is part of the inference model. To get an inference model with a short MCMC, create a test inference model like this:

    inference_model <- create_test_inference_model()
    names(inference_model)
    #> [1] "site_model"        "clock_model"       "tree_prior"
    #> [4] "mrca_prior"        "mcmc"              "beauti_options"
    #> [7] "tipdates_filename"

`mcmc` is the `inference_model` argument to specify the MCMC run options:

    print(inference_model$mcmc$chain_length)
    #> [1] 3000

With these MCMC options, we can now call `bbt_run_from_model` in way that it will finish fast:

    if (is_beast2_installed()) {
      beast2_options <- create_beast2_options()
      out <- bbt_run_from_model(
        fasta_filename = fasta_filename,
        inference_model = inference_model,
        beast2_options = beast2_options
      )
      bbt_delete_temp_files(
        inference_model = inference_model,
        beast2_options = beast2_options
      )
    }

The return value, `out` contains the results of the MCMC run. For this tutorial, visualizing `out` is ignored, as the ‘Demo’ vignette discusses this. Instead, we will work through the other `bbt_run_from_model` parameters.

## `site_model`

`site_model` is the `inference_model` parameter for a site model. As this tutorial works on a DNA alignment, such a site model can also be called a nucleotide substitution model.

Picking a site model is easy: just type:

    create_site_model_

This will trigger auto-complete to show all site models.

The simplest site model is the Jukes-Cantor DNA substitution model. To use this model in `babette`, do:

    inference_model <- create_test_inference_model(
      site_model = create_jc69_site_model()
    )

Using this site model:

    if (is_beast2_installed()) {
      beast2_options <- create_beast2_options()
      out <- bbt_run_from_model(
        fasta_filename = fasta_filename,
        inference_model = inference_model,
        beast2_options = beast2_options
      )
      bbt_delete_temp_files(
        inference_model = inference_model,
        beast2_options = beast2_options
      )
    }

## `clock_model`

`clock_models` is the `inference_model` parameter for a clock model.

Picking a clock model is easy: just type:

    create_clock_model_

This will trigger auto-complete to show all clock models.

The simplest site model is the strict clock model. To use this model in `babette`, do:

    inference_model <- create_test_inference_model(
      clock_model = create_strict_clock_model()
    )

Using this clock model:

    if (is_beast2_installed()) {
      beast2_options <- create_beast2_options()
      out <- bbt_run_from_model(
        fasta_filename = fasta_filename,
        inference_model = inference_model,
        beast2_options = beast2_options
      )
      bbt_delete_temp_files(
        inference_model = inference_model,
        beast2_options = beast2_options
      )
    }

## `tree_prior`

`tree_prior` is the `inference_model` parameter to select a tree prior.

Picking a tree prior is easy: just type:

    create_tree_prior_

This will trigger auto-complete to show all tree priors.

The simplest tree prior is the Yule (pure-birth) tree prior. To use this model in `babette`, do:

    inference_model <- create_test_inference_model(
      tree_prior = create_yule_tree_prior()
    )

Using this tree prior:

    if (is_beast2_installed()) {
      beast2_options <- create_beast2_options()
      out <- bbt_run_from_model(
        fasta_filename = fasta_filename,
        inference_model = inference_model,
        beast2_options = beast2_options
      )
      bbt_delete_temp_files(
        inference_model = inference_model,
        beast2_options = beast2_options
      )
    }

## `mrca_prior`

`mrca_priors` is the `inference_model` parameter to use a Most Recent Common Ancestor (hence, MRCA) prior. With such a prior, it can be specified which taxa have a shared common ancestor and when it existed.

Here is how to specify that the first two taxa in a FASTA file are sister species:

    mrca_prior <- create_mrca_prior(
      alignment_id = get_alignment_id(fasta_filename = fasta_filename),
      taxa_names = get_taxa_names(filename = fasta_filename)[1:2],
      is_monophyletic = TRUE
    )

To specify when the MRCA of all taxa was present, we’ll first create a prior distribution of the crown age, after which we can use that distribution.

To assume the crown age to follow a normal distribution, with a mean of 15.0 (time units), with a standard deviation of 1.0, use `create_normal_distr`:

    mrca_distr <- create_normal_distr(
      mean = 15.0,
      sigma = 1.0
    )

To use that distribution in our MRCA prior:

    mrca_prior <- create_mrca_prior(
      alignment_id = get_alignment_id(fasta_filename = fasta_filename),
      taxa_names = get_taxa_names(filename = fasta_filename),
      mrca_distr = mrca_distr
    )

Using such an MRCA prior:

    inference_model <- create_test_inference_model(
      mrca_prior = mrca_prior
    )

    if (is_beast2_installed()) {
      beast2_options <- create_beast2_options()
      out <- bbt_run_from_model(
        fasta_filename = fasta_filename,
        inference_model = inference_model,
        beast2_options = beast2_options
      )
      bbt_delete_temp_files(
        inference_model = inference_model,
        beast2_options = beast2_options
      )
    }