Package 'greta'

Description

Vectorised is.null

Usage

are_null(x)

Arguments

Value

logical

Examples

is.null(list(NULL, NULL, 1))
are_null(list(NULL, NULL, 1))
are_null(list(NULL, NULL, NULL))
are_null(list(1, 2, 3))
is.null(list(1, 2, 3))

Description

define an object in an R session as a data greta array for use as data in a greta model.

Usage

as_data(x)

Arguments

Details

as_data() can currently convert R objects to greta_arrays if they are numeric or logical vectors, matrices or arrays; or if they are dataframes with only numeric (including integer) or logical elements. Logical elements are always converted to numerics. R objects cannot be converted if they contain missing (NA) or infinite (-Inf or Inf) values.

Examples

## Not run: 

# numeric/integer/logical vectors, matrices and arrays can all be coerced to
# data greta arrays

vec <- rnorm(10)
mat <- matrix(seq_len(3 * 4), nrow = 3)
arr <- array(sample(c(TRUE, FALSE), 2 * 2 * 2, replace = TRUE),
  dim = c(2, 2, 2)
)
(a <- as_data(vec))
(b <- as_data(mat))
(c <- as_data(arr))

# dataframes can also be coerced, provided all the columns are numeric,
# integer or logical
df <- data.frame(
  x1 = rnorm(10),
  x2 = sample(1L:10L),
  x3 = sample(c(TRUE, FALSE), 10, replace = TRUE)
)
(d <- as_data(df))

## End(Not run)

Description

Convert object to a "greta_model" object

Usage

as.greta_model(x, ...)

Arguments

Description

Create objects of class 'unknowns' to nicely print ? valued arrays

Usage

as.unknowns(x)

Arguments

Description

Calculate the values that greta arrays would take, given temporary, or simulated values for the greta arrays on which they depend. This can be used to check the behaviour of your model, make predictions to new data after model fitting, or simulate datasets from either the prior or posterior of your model.

Usage

calculate(
  ...,
  values = list(),
  nsim = NULL,
  seed = NULL,
  precision = c("double", "single"),
  trace_batch_size = 100,
  compute_options = cpu_only()
)

Arguments

Details

The greta arrays named in values need not be variables, they can also be other operations or even data.

At present, if values is a named list it must contain values for all of the variable greta arrays with which target is connected, even values are given for intermediate operations, or the target doesn't depend on the variable. That may be relaxed in a future release.

If the model contains stochastic greta arrays; those with a distribution, calculate can be used to sample from these distributions (and all greta arrays that depend on them) by setting the nsim argument to a positive integer for the required number of samples. If values is specified (either as a list of fixed values or as draws), those values will be used, and remaining variables will be sampled conditional on them. Observed data with distributions (i.e. response variables defined with distribution() can also be sampled, provided they are defined as greta arrays. This behaviour can be used for a number of tasks, like simulating datasets for known parameter sets, simulating parameters and data from a set of priors, or simulating datasets from a model posterior. See some examples of these below.

Value

Values of the target greta array(s), given values of the greta arrays on which they depend (either specified in values or sampled from their priors). If values is a greta_mcmc_list() and nsim = NULL, this will be a greta_mcmc_list object of posterior samples for the target greta arrays. Otherwise, the result will be a named list of numeric R arrays. If nsim = NULL the dimensions of returned numeric R arrays will be the same as the corresponding greta arrays, otherwise an additional dimension with nsim elements will be prepended, to represent multiple simulations.

Examples

## Not run: 

# define a variable greta array, and another that is calculated from it
# then calculate what value y would take for different values of x
x <- normal(0, 1, dim = 3)
a <- lognormal(0, 1)
y <- sum(x^2) + a
calculate(y, values = list(x = c(0.1, 0.2, 0.3), a = 2))

# by setting nsim, you can also sample values from their priors
calculate(y, nsim = 3)

# you can combine sampling and fixed values
calculate(y, values = list(a = 2), nsim = 3)

# if the greta array only depends on data,
# you can pass an empty list to values (this is the default)
x <- ones(3, 3)
y <- sum(x)
calculate(y)

# define a model
alpha <- normal(0, 1)
beta <- normal(0, 1)
sigma <- lognormal(1, 0.1)
y <- as_data(iris$Petal.Width)
mu <- alpha + iris$Petal.Length * beta
distribution(y) <- normal(mu, sigma)
m <- model(alpha, beta, sigma)

# sample values of the parameters, or different observation data (y), from
# the priors (useful for prior # predictive checking) - see also
# ?simulate.greta_model
calculate(alpha, beta, sigma, nsim = 100)
calculate(y, nsim = 100)

# calculate intermediate greta arrays, given some parameter values (useful
# for debugging models)
calculate(mu[1:5], values = list(alpha = 1, beta = 2, sigma = 0.5))
calculate(mu[1:5], values = list(alpha = -1, beta = 0.2, sigma = 0.5))

# simulate datasets given fixed parameter values
calculate(y, values = list(alpha = -1, beta = 0.2, sigma = 0.5), nsim = 10)

# you can use calculate in conjunction with posterior samples from MCMC, e.g.
# sampling different observation datasets, given a random set of these
# posterior samples - useful for posterior predictive model checks
draws <- mcmc(m, n_samples = 500)
calculate(y, values = draws, nsim = 100)

# you can use calculate on greta arrays created even after the inference on
# the model - e.g. to plot response curves
petal_length_plot <- seq(min(iris$Petal.Length),
  max(iris$Petal.Length),
  length.out = 100
)
mu_plot <- alpha + petal_length_plot * beta
mu_plot_draws <- calculate(mu_plot, values = draws)
mu_est <- colMeans(mu_plot_draws[[1]])
plot(mu_est ~ petal_length_plot,
  type = "n",
  ylim = range(mu_plot_draws[[1]])
)
apply(mu_plot_draws[[1]], 1, lines,
  x = petal_length_plot, col = grey(0.8)
)
lines(mu_est ~ petal_length_plot, lwd = 2)

# trace_batch_size can be changed to trade off speed against memory usage
# when calculating. These all produce the same result, but have increasing
# memory requirements:
mu_plot_draws_1 <- calculate(mu_plot,
  values = draws,
  trace_batch_size = 1
)
mu_plot_draws_10 <- calculate(mu_plot,
  values = draws,
  trace_batch_size = 10
)
mu_plot_draws_inf <- calculate(mu_plot,
  values = draws,
  trace_batch_size = Inf
)

## End(Not run)

Description

Compute the Cholesky Factor of a Matrix

Usage

## S3 method for class 'greta_array'
chol(x, ..., force_cholesky = FALSE)

Arguments

Description

Evaluate ⁠t(x) \%*\% x⁠ efficiently, where x is the (upper-triangular) Cholesky factor of a symmetric, positive definite square matrix. I.e. it is the inverse of chol.

Usage

chol2symm(x)

Arguments

Examples

# a symmetric, positive definite square matrix
y <- rWishart(1, 4, diag(3))[, , 1]
y
u <- chol(y)
u
chol2symm(u)
identical(y, chol2symm(u))
identical(chol2symm(u), t(u) %*% u)
## Not run: 
u_greta <- cholesky_variable(3)
y_greta <- chol2symm(u)

## End(Not run)

Description

Sometimes when installing greta you might encounter an error and the best thing to do is start from a clean slate. This function does two things:

1. Removes the "greta-tf2-env" with remove_greta_env()

2. Removes the miniconda installation with remove_miniconda()

Usage

destroy_greta_deps()

Value

nothing

Description

generic to grab dimensions of nodes

Usage

## S3 method for class 'node'
dim(x)

Arguments

Description

set dims like on a matrix/array

Usage

## S3 replacement method for class 'unknowns'
dim(x) <- value

Arguments

Description

distribution defines probability distributions over observed data, e.g. to set a model likelihood.

Usage

distribution(greta_array) <- value

distribution(greta_array)

Arguments

Details

The extract method returns the greta array if it has a distribution, or NULL if it doesn't. It has no real use-case, but is included for completeness

Examples

## Not run: 

# define a model likelihood

# observed data and mean parameter to be estimated
# (explicitly coerce data to a greta array so we can refer to it later)
y <- as_data(rnorm(5, 0, 3))

mu <- uniform(-3, 3)

# define the distribution over y (the model likelihood)
distribution(y) <- normal(mu, 1)

# get the distribution over y
distribution(y)

## End(Not run)

Description

These functions can be used to define random variables in a greta model. They return a variable greta array that follows the specified distribution. This variable greta array can be used to represent a parameter with prior distribution, combined into a mixture distribution using mixture(), or used with distribution() to define a distribution over a data greta array.

Usage

uniform(min, max, dim = NULL)

normal(mean, sd, dim = NULL, truncation = c(-Inf, Inf))

lognormal(meanlog, sdlog, dim = NULL, truncation = c(0, Inf))

bernoulli(prob, dim = NULL)

binomial(size, prob, dim = NULL)

beta_binomial(size, alpha, beta, dim = NULL)

negative_binomial(size, prob, dim = NULL)

hypergeometric(m, n, k, dim = NULL)

poisson(lambda, dim = NULL)

gamma(shape, rate, dim = NULL, truncation = c(0, Inf))

inverse_gamma(alpha, beta, dim = NULL, truncation = c(0, Inf))

weibull(shape, scale, dim = NULL, truncation = c(0, Inf))

exponential(rate, dim = NULL, truncation = c(0, Inf))

pareto(a, b, dim = NULL, truncation = c(0, Inf))

student(df, mu, sigma, dim = NULL, truncation = c(-Inf, Inf))

laplace(mu, sigma, dim = NULL, truncation = c(-Inf, Inf))

beta(shape1, shape2, dim = NULL, truncation = c(0, 1))

cauchy(location, scale, dim = NULL, truncation = c(-Inf, Inf))

chi_squared(df, dim = NULL, truncation = c(0, Inf))

logistic(location, scale, dim = NULL, truncation = c(-Inf, Inf))

f(df1, df2, dim = NULL, truncation = c(0, Inf))

multivariate_normal(mean, Sigma, n_realisations = NULL, dimension = NULL)

wishart(df, Sigma)

lkj_correlation(eta, dimension = 2)

multinomial(size, prob, n_realisations = NULL, dimension = NULL)

categorical(prob, n_realisations = NULL, dimension = NULL)

dirichlet(alpha, n_realisations = NULL, dimension = NULL)

dirichlet_multinomial(size, alpha, n_realisations = NULL, dimension = NULL)

Arguments

Details

The discrete probability distributions (bernoulli, binomial, negative_binomial, poisson, multinomial, categorical, dirichlet_multinomial) can be used when they have fixed values (e.g. defined as a likelihood using distribution(), but not as unknown variables.

For univariate distributions dim gives the dimensions of the greta array to create. Each element of the greta array will be (independently) distributed according to the distribution. dim can also be left at its default of NULL, in which case the dimension will be detected from the dimensions of the parameters (provided they are compatible with one another).

For multivariate distributions (multivariate_normal(), multinomial(), categorical(), dirichlet(), and dirichlet_multinomial()) each row of the output and parameters corresponds to an independent realisation. If a single realisation or parameter value is specified, it must therefore be a row vector (see example). n_realisations gives the number of rows/realisations, and dimension gives the dimension of the distribution. I.e. a bivariate normal distribution would be produced with multivariate_normal(..., dimension = 2). The dimension can usually be detected from the parameters.

multinomial() does not check that observed values sum to size, and categorical() does not check that only one of the observed entries is 1. It's the user's responsibility to check their data matches the distribution!

The parameters of uniform must be fixed, not greta arrays. This ensures these values can always be transformed to a continuous scale to run the samplers efficiently. However, a hierarchical uniform parameter can always be created by defining a uniform variable constrained between 0 and 1, and then transforming it to the required scale. See below for an example.

Wherever possible, the parameterisations and argument names of greta distributions match commonly used R functions for distributions, such as those in the stats or extraDistr packages. The following table states the distribution function to which greta's implementation corresponds:

Examples

## Not run: 

# a uniform parameter constrained to be between 0 and 1
phi <- uniform(min = 0, max = 1)

# a length-three variable, with each element following a standard normal
# distribution
alpha <- normal(0, 1, dim = 3)

# a length-three variable of lognormals
sigma <- lognormal(0, 3, dim = 3)

# a hierarchical uniform, constrained between alpha and alpha + sigma,
eta <- alpha + uniform(0, 1, dim = 3) * sigma

# a hierarchical distribution
mu <- normal(0, 1)
sigma <- lognormal(0, 1)
theta <- normal(mu, sigma)

# a vector of 3 variables drawn from the same hierarchical distribution
thetas <- normal(mu, sigma, dim = 3)

# a matrix of 12 variables drawn from the same hierarchical distribution
thetas <- normal(mu, sigma, dim = c(3, 4))

# a multivariate normal variable, with correlation between two elements
# note that the parameter must be a row vector
Sig <- diag(4)
Sig[3, 4] <- Sig[4, 3] <- 0.6
theta <- multivariate_normal(t(rep(mu, 4)), Sig)

# 10 independent replicates of that
theta <- multivariate_normal(t(rep(mu, 4)), Sig, n_realisations = 10)

# 10 multivariate normal replicates, each with a different mean vector,
# but the same covariance matrix
means <- matrix(rnorm(40), 10, 4)
theta <- multivariate_normal(means, Sig, n_realisations = 10)
dim(theta)

# a Wishart variable with the same covariance parameter
theta <- wishart(df = 5, Sigma = Sig)

## End(Not run)

Description

Generic methods to extract and replace elements of greta arrays, or to combine greta arrays.

Arguments

Details

diag() can be used to extract or replace the diagonal part of a square and two-dimensional greta array, but it cannot be used to create a matrix-like greta array from a scalar or vector-like greta array. A static diagonal matrix can always be created with e.g. diag(3), and then converted into a greta array.

Also note that since R 4.0.0, head and tail methods for arrays changed to print a vector rather than maintain the array structure. The greta package supports both methods, and will do so based on which version of R you are using.

Usage

# extract
x[i]
x[i, j, ..., drop = FALSE]
head(x, n = 6L, ...)
tail(x, n = 6L, ...)
diag(x, nrow, ncol)

# replace
x[i] <- value
x[i, j, ...] <- value
diag(x) <- value

# combine
cbind(...)
rbind(...)
abind(...)
c(..., recursive = FALSE)
rep(x, times, ..., recursive = FALSE)

# get and set dimensions
length(x)
dim(x)
dim(x) <- value

Examples

## Not run: 

x <- as_data(matrix(1:12, 3, 4))

# extract and replace
x[1:3, ]
x[, 2:4] <- 1:9
e <- diag(x)
diag(x) <- e + 1

# combine
cbind(x[, 2], x[, 1])
rbind(x[1, ], x[3, ])
abind(x[1, ], x[3, ], along = 1)
c(x[, 1], x)
rep(x[, 2], times = 3)

## End(Not run)

Description

This is a list of functions (mostly from base R) that are currently implemented to transform greta arrays. Also see operators and transforms.

Details

TensorFlow only enables rounding to integers, so round() will error if digits is set to anything other than 0.

Any additional arguments to chol(), chol2inv, solve(), and log() will be ignored, see the TensorFlow documentation for details of these routines.

sweep() only works on two-dimensional greta arrays (so MARGIN can only be either 1 or 2), and only for subtraction, addition, division and multiplication.

tapply() works on column vectors (2D greta arrays with one column), and INDEX cannot be a greta array. Currently five functions are available, and arguments passed to ... are ignored.

cospi(), sinpi(), and tanpi() do not use the computationally more stable routines to compute cos(x * pi) etc. that are available in R under some operating systems. Similarly trigamma() uses TensorFlow's polygamma function, resulting in lower precision than R's equivalent.

Usage

 # logarithms and exponentials
 log(x)
 exp(x)
 log1p(x)
 expm1(x)

 # miscellaneous mathematics
 abs(x)
 mean(x)
 sqrt(x)
 sign(x)

 # rounding of numbers
 ceiling(x)
 floor(x)
 round(x, digits = 0)

 # trigonometry
 cos(x)
 sin(x)
 tan(x)
 acos(x)
 asin(x)
 atan(x)
 cosh(x)
 sinh(x)
 tanh(x)
 acosh(x)
 asinh(x)
 atanh(x)
 cospi(x)
 sinpi(x)
 tanpi(x)

 # special mathematical functions
 lgamma(x)
 digamma(x)
 trigamma(x)
 choose(n, k)
 lchoose(n, k)

 # matrix operations
 t(x)
 chol(x, ...)
 chol2inv(x, ...)
 cov2cor(V)
 solve(a, b, ...)
 kronecker(X, Y, FUN = c('*', '/', '+', '-'))

 # reducing operations
 sum(..., na.rm = TRUE)
 prod(..., na.rm = TRUE)
 min(..., na.rm = TRUE)
 max(..., na.rm = TRUE)

 # cumulative operations
 cumsum(x)
 cumprod(x)
 cummax(x)
 cummin(x)

 # solve an upper or lower triangular system
 backsolve(r, x, k = ncol(r), upper.tri = TRUE,
           transpose = FALSE)
 forwardsolve(l, x, k = ncol(l), upper.tri = FALSE,
              transpose = FALSE)

 # miscellaneous operations
 aperm(x, perm)
 apply(x, MARGIN, FUN = c("sum", "max", "mean", "min",
                          "prod", "cumsum", "cumprod"))
 sweep(x, MARGIN, STATS, FUN = c('-', '+', '/', '*'))
 tapply(X, INDEX, FUN = c("sum", "max", "mean", "min", "prod"), ...)

Examples

## Not run: 

x <- as_data(matrix(1:9, nrow = 3, ncol = 3))
a <- log(exp(x))
b <- log1p(expm1(x))
c <- sign(x - 5)
d <- abs(x - 5)

z <- t(a)

y <- sweep(x, 1, e, "-")

## End(Not run)

Description

These functions set the use of CPU or GPU inside of greta. They simply return either "GPU" or "CPU", but in the future may handle more complexity. These functions are passed to compute_options inside of a few functions: mcmc(), opt(), and calculate().

Usage

gpu_only()

cpu_only()

Description

greta lets you write statistical models interactively in native R code, then sample from them efficiently using Hamiltonian Monte Carlo.

The computational heavy lifting is done by TensorFlow, Google's automatic differentiation library. So greta is particularly fast where the model contains lots of linear algebra, and greta models can be run across CPU clusters or on GPUs.

See the simple example below, and take a look at the greta website for more information including tutorials and examples.

Author(s)

Maintainer: Nicholas Tierney [email protected] (ORCID)

Authors:

• Nick Golding [email protected] (ORCID)

Other contributors:

• Simon Dirmeier [contributor]

• Adam Fleischhacker [contributor]

• Shirin Glander [contributor]

• Martin Ingram [contributor]

• Lee Hazel [contributor]

• Lionel Hertzog [contributor]

• Tiphaine Martin [contributor]

• Matt Mulvahill [contributor]

• Michael Quinn [contributor]

• David Smith [contributor]

• Paul Teetor [contributor]

• Jian Yen [contributor]

See Also

Useful links:

• https://greta-stats.org

• https://github.com/greta-dev/greta

• Report bugs at https://github.com/greta-dev/greta/issues

Examples

## Not run: 
# a simple Bayesian regression model for the iris data

# priors
int <- normal(0, 5)
coef <- normal(0, 3)
sd <- lognormal(0, 3)

# likelihood
mean <- int + coef * iris$Petal.Length
distribution(iris$Sepal.Length) <- normal(mean, sd)

# build and sample
m <- model(int, coef, sd)
draws <- mcmc(m, n_samples = 100)

## End(Not run)

Description

This function runs reticulate::conda_create() inside callr::r_process_options(), to create the conda environment, "greta-env-tf2". This is used within install_greta_deps() as part of setting up python dependencies. It uses a version of python that is compatible with the versions of tensorflow and tensorflow-probability, which is established with greta_deps_spec(). We mostly recommend users use install_greta_deps() to manage their python dependency installation.

Usage

greta_create_conda_env(timeout = 5, deps = greta_deps_spec())

Arguments

Value

nothing - creates a conda environment for a specific python version

Description

To assist with capturing and sharing python dependencies, we provide a way to capture the dependencies currently used.

Usage

greta_deps_receipt()

Value

greta_deps_spec() object

Examples

## Not run: 
my_deps <- greta_deps_receipt()

## End(Not run)

Description

A helper function for specifying versions of Tensorflow (TF), Tensorflow Probability (TFP), and Python. Defaulting to 2.15.0, 0.23.0, and 3.10, respectively. You can specify the version that you want to install, but it will check if these are compatible. That is, if you specify versions of TF/TFP/Python which do not work with each other, it will error and give a suggested version to install. It does this by using a dataset, greta_deps_tf_tfp, to check if the versions of TF, TFP, and Python specified are compatible on your operating system. You can inspect this dataset with View(greta_deps_tf_tfp).

Usage

greta_deps_spec(
  tf_version = "2.15.0",
  tfp_version = "0.23.0",
  python_version = "3.10"
)

Arguments

Value

data frame of valid dependencies

Examples

greta_deps_spec()
greta_deps_spec(tf_version = "2.15.0")
greta_deps_spec(tf_version = "2.15.0", tfp_version = "0.23.0")
greta_deps_spec(tf_version = "2.15.0", python_version = "3.10")
greta_deps_spec(
  tf_version = "2.15.0",
  tfp_version = "0.23.0",
  python_version = "3.10"
  )
# this will fail
## Not run: 
greta_deps_spec(
  tf_version = "2.11.0",
  tfp_version = "0.23.0",
  python_version = "3.10"
  )
  
## End(Not run)

Description

This is a dataset that contains suggested valid versions of Tensorflow (TF), Tensorflow Probability (TFP), and Python for linux, mac, and windows machines. It was constructed from https://www.tensorflow.org/install/source and https://www.tensorflow.org/install/source_windows, and by inspecting https://github.com/tensorflow/probability/releases.

Usage

greta_deps_tf_tfp

Format

greta_deps_tf_tfp

A data frame with 63 rows and 5 columns:

os

Operating System

tfp_version, tf_version

numeric versions in format major.minor.patch for TFP and TF

python_version_min, python_version_max

numeric versions range in format major.minor.patch for Python

Details

We recommend using the default versions provided in greta_deps_spec().

Description

This installs miniconda using reticulate::install_miniconda() inside callr::r_process_options(). Used internally by install_greta_deps(). We mostly recommend users use install_greta_deps() to manage their python dependency installation.

Usage

greta_install_miniconda(timeout = 5)

Arguments

Value

nothing - installs miniconda.

Description

These functions retrieve specific python error messages that might come up during greta use.

Usage

greta_notes_tf_num_error()

Examples

## Not run: 
greta_notes_tf_error()

## End(Not run)

Description

To help debug greta installation, you can save all installation output to a single logfile.

Usage

greta_set_install_logfile(path)

Arguments

Value

nothing - sets an environment variable for use with install_greta_deps().

Description

This checks if Python, Tensorflow, Tensorflow Probability, and the greta conda environment are available, and also loads and initialises python

Usage

greta_sitrep()

Value

Message if greta is ready to use

Examples

## Not run: 
greta_sitrep()

## End(Not run)

Description

Carry out statistical inference on greta models by MCMC or likelihood/posterior optimisation.

Usage

mcmc(
  model,
  sampler = hmc(),
  n_samples = 1000,
  thin = 1,
  warmup = 1000,
  chains = 4,
  n_cores = NULL,
  verbose = TRUE,
  pb_update = 50,
  one_by_one = FALSE,
  initial_values = initials(),
  trace_batch_size = 100,
  compute_options = cpu_only()
)

stashed_samples()

extra_samples(
  draws,
  n_samples = 1000,
  thin = 1,
  n_cores = NULL,
  verbose = TRUE,
  pb_update = 50,
  one_by_one = FALSE,
  trace_batch_size = 100,
  compute_options = cpu_only()
)

initials(...)

opt(
  model,
  optimiser = bfgs(),
  max_iterations = 100,
  tolerance = 1e-06,
  initial_values = initials(),
  adjust = TRUE,
  hessian = FALSE,
  compute_options = cpu_only()
)

Arguments

Details

For mcmc() if verbose = TRUE, the progress bar shows the number of iterations so far and the expected time to complete the phase of model fitting (warmup or sampling). Occasionally, a proposed set of parameters can cause numerical instability (I.e. the log density or its gradient is NA, Inf or -Inf); normally because the log joint density is so low that it can't be represented as a floating point number. When this happens, the progress bar will also display the proportion of proposals so far that were 'bad' (numerically unstable) and therefore rejected. Some numerical instability during the warmup phase is normal, but 'bad' samples during the sampling phase can lead to bias in your posterior sample. If you only have a few bad samples (<10\%), you can usually resolve this with a longer warmup period or by manually defining starting values to move the sampler into a more reasonable part of the parameter space. If you have more samples than that, it may be that your model is misspecified. You can often diagnose this by using calculate() to evaluate the values of greta arrays, given fixed values of model parameters, and checking the results are what you expect.

greta runs multiple chains simultaneously with a single sampler, vectorising all operations across the chains. E.g. a scalar addition in your model is computed as an elementwise vector addition (with vectors having length chains), a vector addition is computed as a matrix addition etc. TensorFlow is able to parallelise these operations, and this approach reduced computational overheads, so this is the most efficient of computing on multiple chains.

Multiple mcmc samplers (each of which can simultaneously run multiple chains) can also be run in parallel by setting the execution plan with the future package. Only plan(multisession) futures or plan(cluster) futures that don't use fork clusters are allowed, since forked processes conflict with TensorFlow's parallelism. Explicitly parallelising chains on a local machine with plan(multisession) will probably be slower than running multiple chains simultaneously in a single sampler (with plan(sequential), the default) because of the overhead required to start new sessions. However, plan(cluster) can be used to run chains on a cluster of machines on a local or remote network. See future::cluster() for details, and the future.batchtools package to set up plans on clusters with job schedulers.

If n_cores = NULL and mcmc samplers are being run sequentially, each sampler will be allowed to use all CPU cores (possibly to compute multiple chains sequentially). If samplers are being run in parallel with the future package, n_cores will be set so that ⁠n_cores * [future::nbrOfWorkers]⁠ is less than the number of CPU cores.

After carrying out mcmc on all the model parameters, mcmc() calculates the values of (i.e. traces) the parameters of interest for each of these samples, similarly to calculate(). Multiple posterior samples can be traced simultaneously, though this can require large amounts of memory for large models. As in calculate, the argument trace_batch_size can be modified to trade-off speed against memory usage.

If the sampler is aborted before finishing (and future parallelism isn't being used), the samples collected so far can be retrieved with stashed_samples(). Only samples from the sampling phase will be returned.

Samples returned by mcmc() and stashed_samples() can be added to with extra_samples(). This continues the chain from the last value of the previous chain and uses the same sampler and model as was used to generate the previous samples. It is not possible to change the sampler or extend the warmup period.

Because opt() acts on a list of greta arrays with possibly varying dimension, the par and hessian objects returned by opt() are named lists, rather than a vector (par) and a matrix (hessian), as returned by stats::optim(). Because greta arrays may not be vectors, the Hessians may not be matrices, but could be higher-dimensional arrays. To return a Hessian matrix covering multiple model parameters, you can construct your model so that all those parameters are in a vector, then split the vector up to define the model. The parameter vector can then be passed to model. See example.

Value

mcmc, stashed_samples & extra_samples - a greta_mcmc_list object that can be analysed using functions from the coda package. This will contain mcmc samples of the greta arrays used to create model.

opt - a list containing the following named elements:

• par a named list of the optimal values for the greta arrays specified in model

• value the (unadjusted) negative log joint density of the model at the parameters 'par'

• iterations the number of iterations taken by the optimiser

• convergence an integer code, 0 indicates successful completion, 1 indicates the iteration limit max_iterations had been reached

• hessian (if hessian = TRUE) a named list of hessian matrices/arrays for the parameters (w.r.t. value)

Note

to set a seed with MCMC you can use set.seed(), or tensorflow::set_random_seed(). They both given identical results. See examples below.

Examples

## Not run: 
# define a simple Bayesian model
x <- rnorm(10)
mu <- normal(0, 5)
sigma <- lognormal(1, 0.1)
distribution(x) <- normal(mu, sigma)
m <- model(mu, sigma)

# carry out mcmc on the model
draws <- mcmc(m, n_samples = 100)

# add some more samples
draws <- extra_samples(draws, 200)

#' # initial values can be passed for some or all model variables
draws <- mcmc(m, chains = 1, initial_values = initials(mu = -1))

# if there are multiple chains, a list of initial values should be passed,
# othewise the same initial values will be used for all chains
inits <- list(initials(sigma = 0.5), initials(sigma = 1))
draws <- mcmc(m, chains = 2, initial_values = inits)

# you can auto-generate a list of initials with something like this:
inits <- replicate(4,
  initials(mu = rnorm(1), sigma = runif(1)),
  simplify = FALSE
)
draws <- mcmc(m, chains = 4, initial_values = inits)

# or find the MAP estimate
opt_res <- opt(m)

# get the MLE of the normal variance
mu <- variable()
variance <- variable(lower = 0)
distribution(x) <- normal(mu, sqrt(variance))
m2 <- model(variance)

# adjust = FALSE skips the jacobian adjustments used in MAP estimation, to
# give the true maximum likelihood estimates
o <- opt(m2, adjust = FALSE)

# the MLE corresponds to the *unadjusted* sample variance, but differs
# from the sample variance
o$par
mean((x - mean(x))^2) # same
var(x) # different

# initial values can also be passed to optimisers:
o <- opt(m2, initial_values = initials(variance = 1))

# and you can return a list of the Hessians for each of these parameters
o <- opt(m2, hessian = TRUE)
o$hessian


# to get a hessian matrix across multiple greta arrays, you must first
# combine them and then split them up for use in the model (so that the
# combined vector is part of the model) and pass that vector to model:
params <- c(variable(), variable(lower = 0))
mu <- params[1]
variance <- params[2]
distribution(x) <- normal(mu, sqrt(variance))
m3 <- model(params)
o <- opt(m3, hessian = TRUE)
o$hessian

# using set.seed or tensorflow::set_random_seed to set RNG for MCMC
a <- normal(0, 1)
y <- normal(a, 1)
m <- model(y)

set.seed(12345)
one <- mcmc(m, n_samples = 1, chains = 1)
set.seed(12345)
two <- mcmc(m, n_samples = 1, chains = 1)
# same
all.equal(as.numeric(one), as.numeric(two))
tensorflow::set_random_seed(12345)
one_tf <- mcmc(m, n_samples = 1, chains = 1)
tensorflow::set_random_seed(12345)
two_tf <- mcmc(m, n_samples = 1, chains = 1)
# same
all.equal(as.numeric(one_tf), as.numeric(two_tf))
# different
all.equal(as.numeric(one), as.numeric(one_tf))


## End(Not run)

Description

This is a helper function to install Python dependencies needed. By default these are TF 2.15.0, TFP 0.23.0, and Python 3.10. These Python modules will be installed into a conda environment named "greta-env-tf2".

Usage

install_greta_deps(
  deps = greta_deps_spec(),
  timeout = 5,
  restart = c("ask", "force", "no"),
  ...
)

reinstall_greta_deps(
  deps = greta_deps_spec(),
  timeout = 5,
  restart = c("ask", "force", "no")
)

Arguments

Details

You can specify an environment variable to write a logfile to a specific location with GRETA_INSTALLATION_LOG using Sys.setenv('GRETA_INSTALLATION_LOG'='path/to/logfile.html'). Or use greta_set_install_logfile() to set the path, e.g., greta_set_install_logfile('path/to/logfile.html'). By default it uses tools::R_user_dir("greta") as the directory to save a logfile named "greta-installation-logfile.html". To see installation notes or errors, after installation you can open the logfile with open_greta_install_log(), or you can navigate to the logfile and open it in a browser.

By default, if using RStudio, it will now ask you if you want to restart the R session. If the session is not interactive, or is not in RStudio, it will not restart. You can also override this with restart = TRUE.

Note

This will automatically install Miniconda (a minimal version of the Anaconda scientific software management system), create a 'conda' environment for greta named 'greta-env-tf2' with required python and python package versions, and forcibly switch over to using that conda environment.

If you don't want to use conda or the "greta-env-tf2" conda environment, you can install versions that you like, e.g., using reticulate::py_install(). If you want to see which versions of TF, TFP, and Python work with each other (at least according to information from tensorflows website), see the data greta_deps_tf_tfp, which is provided with greta. Managing your own installation is not always straightforward, so we recommend installing the python packages using install_greta_deps() for most users.

Examples

## Not run: 
install_greta_deps()

## End(Not run)
## Not run: 
# to help troubleshoot your greta installation, this can help resolve some
# issues with installing greta dependencies
reinstall_greta_deps()

## End(Not run)

Description

A list of functions and R6 class objects that can be used to develop extensions to greta. Most users will not need to access these methods, and it is not recommended to use them directly in model code.

Details

This help file lists the available internals, but they are not fully documented and are subject to change and deprecation without warning (though care will be taken not to break dependent packages on CRAN). For an overview of how greta works internally, see the technical details vignette. See https://github.com/greta-dev for examples of R packages extending and building on greta.

Please get in contact via GitHub if you want to develop an extension to greta and need more details of how to use these internal functions.

You can use attach() to put a sublist in the search path. E.g. attach(.internals$nodes$constructors) will enable you to call op(), vble() and distrib() directly.

Usage

 .internals$greta_arrays$unknowns        # greta array print methods
 .internals$inference$progress_bar       # progress bar tools
                      samplers           # MCMC samplers
                      stash              # stashing MCMC samples
 .internals$nodes$constructors           # node creation wrappers
                  distribution_classes   # R6 distribution classes
                  mixture_classes        # R6 mixture distribution classes
                  node_classes           # R6 node classes
 .internals$tensors                      # functions on tensors
 .internals$utils$checks                 # checking function inputs
                  colours                # greta colour scheme
                  dummy_arrays           # mocking up extract/replace
                  misc                   # code simplification etc.
                  samplers               # mcmc helpers
 .internals$greta_stash                  # internal information storage

Description

Is object a greta array?

Usage

is.greta_array(x, ...)

Arguments

Description

Is object a greta_mcmc_list?

Usage

is.greta_mcmc_list(x, ...)

Arguments

Value

logical TRUE/FALSE

Description

joint combines univariate probability distributions together into a multivariate (and a priori independent between dimensions) joint distribution, either over a variable, or for fixed data.

Usage

joint(..., dim = NULL)

Arguments

Details

The component probability distributions must all be either continuous or discrete, and must have the same dimensions.

This functionality is unlikely to be useful in most models, since the same result can usually be achieved by combining variables with separate distributions. It is included for situations where it is more convenient to consider these as a single distribution, e.g. for use with distribution or mixture.

Examples

## Not run: 
# an uncorrelated bivariate normal
x <- joint(normal(-3, 0.5), normal(3, 0.5))
m <- model(x)
plot(mcmc(m, n_samples = 500))

# joint distributions can be used to define densities over data
x <- cbind(rnorm(10, 2, 0.5), rbeta(10, 3, 3))
mu <- normal(0, 10)
sd <- normal(0, 3, truncation = c(0, Inf))
a <- normal(0, 3, truncation = c(0, Inf))
b <- normal(0, 3, truncation = c(0, Inf))
distribution(x) <- joint(normal(mu, sd), beta(a, b),
  dim = 10
)
m <- model(mu, sd, a, b)
plot(mcmc(m))

## End(Not run)

Description

mixture combines other probability distributions into a single mixture distribution, either over a variable, or for fixed data.

Usage

mixture(..., weights, dim = NULL)

Arguments

Details

The weights are rescaled to sum to one along the first dimension, and are then used as the mixing weights of the distribution. I.e. the probability density is calculated as a weighted sum of the component probability distributions passed in via ⁠\dots⁠

The component probability distributions must all be either continuous or discrete, and must have the same dimensions.

Examples

## Not run: 
# a scalar variable following a strange bimodal distibution
weights <- uniform(0, 1, dim = 3)
a <- mixture(normal(-3, 0.5),
  normal(3, 0.5),
  normal(0, 3),
  weights = weights
)
m <- model(a)
plot(mcmc(m, n_samples = 500))

# simulate a mixture of poisson random variables and try to recover the
# parameters with a Bayesian model
x <- c(
  rpois(800, 3),
  rpois(200, 10)
)

weights <- uniform(0, 1, dim = 2)
rates <- normal(0, 10, truncation = c(0, Inf), dim = 2)
distribution(x) <- mixture(poisson(rates[1]),
  poisson(rates[2]),
  weights = weights
)
m <- model(rates)
draws_rates <- mcmc(m, n_samples = 500)

# check the mixing probabilities after fitting using calculate()
# (you could also do this within the model)
normalized_weights <- weights / sum(weights)
draws_weights <- calculate(normalized_weights, draws_rates)

# get the posterior means
summary(draws_rates)$statistics[, "Mean"]
summary(draws_weights)$statistics[, "Mean"]

# weights can also be an array, giving different mixing weights
# for each observation (first dimension must be number of components)
dim <- c(5, 4)
weights <- uniform(0, 1, dim = c(2, dim))
b <- mixture(normal(1, 1, dim = dim),
  normal(-1, 1, dim = dim),
  weights = weights
)

## End(Not run)

Description

Create a greta_model object representing a statistical model (using model), and plot a graphical representation of the model. Statistical inference can be performed on greta_model objects with mcmc()

Usage

model(..., precision = c("double", "single"), compile = TRUE)

## S3 method for class 'greta_model'
print(x, ...)

## S3 method for class 'greta_model'
plot(x, y, colour = "#996bc7", ...)

Arguments

Details

model() takes greta arrays as arguments, and defines a statistical model by finding all of the other greta arrays on which they depend, or which depend on them. Further arguments to model can be used to configure the TensorFlow graph representing the model, to tweak performance.

The plot method produces a visual representation of the defined model. It uses the DiagrammeR package, which must be installed first. Here's a key to the plots:

Value

model - a greta_model object.

plot - a DiagrammeR::grViz() object, with the DiagrammeR::dgr_graph() object used to create it as an attribute "dgr_graph".

Examples

## Not run: 

# define a simple model
mu <- variable()
sigma <- normal(0, 3, truncation = c(0, Inf))
x <- rnorm(10)
distribution(x) <- normal(mu, sigma)

m <- model(mu, sigma)

plot(m)

## End(Not run)

Description

This is a convenience function to facilitate reading logfiles. It opens a HTML browser using utils::browseURL(). It will search for the environment variable "GRETA_INSTALLATION_LOG" or default to tools::R_user_dir("greta"). To set "GRETA_INSTALLATION_LOG" you can use Sys.setenv('GRETA_INSTALLATION_LOG'='path/to/logfile.html'). Or use greta_set_install_logfile() to set the path, e.g., greta_set_install_logfile('path/to/logfile.html').

Usage

open_greta_install_log()

Value

opens a URL in your default HTML browser.

Description

This is a list of currently implemented arithmetic, logical and relational operators to combine greta arrays into probabilistic models. Also see functions and transforms.

Details

greta's operators are used just like R's the standard arithmetic, logical and relational operators, but they return other greta arrays. Since the operations are only carried during sampling, the greta array objects have unknown values.

Usage

 # arithmetic operators
 -x
 x + y
 x - y
 x * y
 x / y
 x ^ y
 x %% y
 x %/% y
 x %*% y

 # logical operators
 !x
 x & y
 x | y

 # relational operators
 x < y
 x > y
 x <= y
 x >= y
 x == y
 x != y
 

Examples

## Not run: 

x <- as_data(-1:12)

# arithmetic
a <- x + 1
b <- 2 * x + 3
c <- x %% 2
d <- x %/% 5

# logical
e <- (x > 1) | (x < 1)
f <- e & (x < 2)
g <- !f

# relational
h <- x < 1
i <- (-x) >= x
j <- h == x

## End(Not run)

Description

Functions to set up optimisers (which find parameters that maximise the joint density of a model) and change their tuning parameters, for use in opt(). For details of the algorithms and how to tune them, see the TensorFlow optimiser docs, or the Tensorflow Probability optimiser docs.

Usage

nelder_mead(
  objective_function = NULL,
  initial_vertex = NULL,
  step_sizes = NULL,
  func_tolerance = 1e-08,
  position_tolerance = 1e-08,
  reflection = NULL,
  expansion = NULL,
  contraction = NULL,
  shrinkage = NULL
)

bfgs(
  value_and_gradients_function = NULL,
  initial_position = NULL,
  tolerance = 1e-08,
  x_tolerance = 0L,
  f_relative_tolerance = 0L,
  initial_inverse_hessian_estimate = NULL,
  stopping_condition = NULL,
  validate_args = TRUE,
  max_line_search_iterations = 50L,
  f_absolute_tolerance = 0L
)

powell()

momentum()

cg()

newton_cg()

l_bfgs_b()

tnc()

cobyla()

slsqp()

gradient_descent(learning_rate = 0.01, momentum = 0, nesterov = FALSE)

adadelta(learning_rate = 0.001, rho = 1, epsilon = 1e-08)

adagrad(learning_rate = 0.8, initial_accumulator_value = 0.1, epsilon = 1e-08)

adagrad_da(
  learning_rate = 0.8,
  global_step = 1L,
  initial_gradient_squared_accumulator_value = 0.1,
  l1_regularization_strength = 0,
  l2_regularization_strength = 0
)

adam(
  learning_rate = 0.1,
  beta_1 = 0.9,
  beta_2 = 0.999,
  amsgrad = FALSE,
  epsilon = 1e-08
)

adamax(learning_rate = 0.001, beta_1 = 0.9, beta_2 = 0.999, epsilon = 1e-07)

ftrl(
  learning_rate = 1,
  learning_rate_power = -0.5,
  initial_accumulator_value = 0.1,
  l1_regularization_strength = 0,
  l2_regularization_strength = 0,
  l2_shrinkage_regularization_strength = 0,
  beta = 0
)

proximal_gradient_descent(
  learning_rate = 0.01,
  l1_regularization_strength = 0,
  l2_regularization_strength = 0
)

proximal_adagrad(
  learning_rate = 1,
  initial_accumulator_value = 0.1,
  l1_regularization_strength = 0,
  l2_regularization_strength = 0
)

nadam(learning_rate = 0.001, beta_1 = 0.9, beta_2 = 0.999, epsilon = 1e-07)

rms_prop(
  learning_rate = 0.1,
  rho = 0.9,
  momentum = 0,
  epsilon = 1e-10,
  centered = FALSE
)

Arguments

Details

The optimisers powell(), cg(), newton_cg(), l_bfgs_b(), tnc(), cobyla(), and slsqp() are now defunct. They will error when called in greta 0.5.0. This are removed because they are no longer available in TensorFlow 2.0. Note that optimiser momentum() has been replaced with gradient_descent()

Value

an optimiser object that can be passed to opt().

Note

This optimizer isn't supported in TF2, so proceed with caution. See the TF docs on AdagradDAOptimiser for more detail.

This optimizer isn't supported in TF2, so proceed with caution. See the TF docs on ProximalGradientDescentOptimizer for more detail.

This optimizer isn't supported in TF2, so proceed with caution. See the TF docs on ProximalAdagradOptimizer for more detail.

Examples

## Not run: 
# use optimisation to find the mean and sd of some data
x <- rnorm(100, -2, 1.2)
mu <- variable()
sd <- variable(lower = 0)
distribution(x) <- normal(mu, sd)
m <- model(mu, sd)

# configure optimisers & parameters via 'optimiser' argument to opt
opt_res <- opt(m, optimiser = bfgs())

# compare results with the analytic solution
opt_res$par
c(mean(x), sd(x))

## End(Not run)

Description

greta provides a wide range of methods to apply common R functions and operations to greta_array objects. A few of these functions and operators are not associated with a class system, so they are overloaded here. This should not affect normal use of these functions, but they need to be documented to satisfy CRAN's check.

Usage

x %*% y

chol2inv(x, size = NCOL(x), LINPACK = FALSE)

cov2cor(V)

identity(x)

colMeans(x, na.rm = FALSE, dims = 1L)

rowMeans(x, na.rm = FALSE, dims = 1L)

colSums(x, na.rm = FALSE, dims = 1L)

rowSums(x, na.rm = FALSE, dims = 1L)

sweep(x, MARGIN, STATS, FUN = "-", check.margin = TRUE, ...)

backsolve(r, x, k = ncol(r), upper.tri = TRUE, transpose = FALSE)

forwardsolve(l, x, k = ncol(l), upper.tri = FALSE, transpose = FALSE)

apply(X, MARGIN, FUN, ...)

tapply(X, INDEX, FUN, ...)

eigen(x, symmetric, only.values, EISPACK)

rdist(x1, x2 = NULL, compact = FALSE)

abind(
  ...,
  along = N,
  rev.along = NULL,
  new.names = NULL,
  force.array = TRUE,
  make.names = use.anon.names,
  use.anon.names = FALSE,
  use.first.dimnames = FALSE,
  hier.names = FALSE,
  use.dnns = FALSE
)

diag(x = 1, nrow, ncol)

Arguments

Details

Note that, since R 3.1, the LINPACK argument is defunct and silently ignored. The argument is only included for compatibility with the base functions that call it.

To find the original help file for these overloaded functions, search for the function, e.g., ?cov2cor and select the non-greta function.

Description

Print method for greta python deps

Usage

## S3 method for class 'greta_deps_spec'
print(x, ...)

Arguments

Description

Print method for greta MCMC list

Usage

## S3 method for class 'greta_mcmc_list'
print(x, ..., n = 5)

Arguments

Value

printed MCMC output

Description

This can be useful when debugging greta installation to get to "clean slate". There are four functions:

Usage

remove_greta_env()

reinstall_greta_env(timeout = 5)

remove_miniconda()

reinstall_miniconda(timeout = 5)

Arguments

Details

• remove_greta_env() removes the 'greta-env-tf2' conda environment

• remove_miniconda() removes miniconda installation

• reinstall_greta_env() remove 'greta-env-tf2' and reinstall it using greta_create_conda_env() (which is used internally).

• reinstall_miniconda() removes miniconda and reinstalls it using greta_install_miniconda() (which is used internally)

Value

invisible

See Also

destroy_greta_deps()

Examples

## Not run: 
remove_greta_env()
remove_miniconda()
reinstall_greta_env()
reinstall_miniconda()

## End(Not run)

Description

Should also allow for building other methods in the future

Usage

run_optimiser(self)

Arguments

Description

Functions to set up MCMC samplers and change the starting values of their parameters, for use in mcmc().

Usage

hmc(Lmin = 5, Lmax = 10, epsilon = 0.1, diag_sd = 1)

rwmh(proposal = c("normal", "uniform"), epsilon = 0.1, diag_sd = 1)

slice(max_doublings = 5)

Arguments

Details

During the warmup iterations of mcmc, some of these sampler parameters will be tuned to improve the efficiency of the sampler, so the values provided here are used as starting values.

For hmc(), the number of leapfrog steps at each iteration is selected uniformly at random from between Lmin and Lmax. diag_sd is used to rescale the parameter space to make it more uniform, and make sampling more efficient.

rwmh() creates a random walk Metropolis-Hastings sampler; a a gradient-free sampling algorithm. The algorithm involves a proposal generating step proposal_state = current_state + perturb by a random perturbation, followed by Metropolis-Hastings accept/reject step. The class is implemented for uniform and normal proposals.

slice() implements a multivariate slice sampling algorithm. The parameter max_doublings is not tuned during warmup.

Value

a sampler object that can be passed to mcmc().

Description

Simulate values of all named greta arrays associated with a greta model from the model priors, including the response variable.

Usage

## S3 method for class 'greta_model'
simulate(object, nsim = 1, seed = NULL, precision = c("double", "single"), ...)

Arguments

Details

This is essentially a wrapper around calculate() that finds all relevant greta arrays. See that function for more functionality, including simulation conditional on fixed values or posterior samples.

To simulate values of the response variable, it must be both a named object (in the calling environment) and be a greta array. If you don't see it showing up in the output, you may need to use as_data to convert it to a greta array before defining the model.

Value

A named list of vectors, matrices or arrays containing independent samples of the greta arrays associated with the model. The number of samples will be prepended as the first dimension of the greta array, so that a vector of samples is returned for each scalar greta array, and a matrix is returned for each vector greta array, etc.

Examples

## Not run: 
# build a greta model
n <- 10
y <- rnorm(n)
y <- as_data(y)

library(greta)
sd <- lognormal(1, 2)
mu <- normal(0, 1, dim = n)
distribution(y) <- normal(mu, sd)
m <- model(mu, sd)

# simulate one random draw of y, mu and sd from the model prior:
sims <- simulate(m)

# 100 simulations of y, mu and sd
sims <- simulate(m, nsim = 100)

## End(Not run)
# nolint start

Description

These structures can be used to set up more complex models. For example, scalar parameters can be embedded in a greta array by first creating a greta array with zeros() or ones(), and then embedding the parameter value using greta's replacement syntax.

Usage

zeros(...)

ones(...)

greta_array(data = 0, dim = length(data))

Arguments

Details

greta_array is a convenience function to create an R array with array() and then coerce it to a greta array. I.e. when passed something that can be coerced to a numeric array, it is equivalent to as_data(array(data, dim)).

If data is a greta array and dim is different than dim(data), a reshaped greta array is returned. This is equivalent to: dim(data) <- dim.

Value

a greta array object

Examples

## Not run: 

# a 3 row, 4 column greta array of 0s
z <- zeros(3, 4)

# a 3x3x3 greta array of 1s
z <- ones(3, 3, 3)

# a 2x4 greta array filled with pi
z <- greta_array(pi, dim = c(2, 4))

# a 3x3x3 greta array filled with 1, 2, and 3
z <- greta_array(1:3, dim = c(3, 3, 3))

## End(Not run)

Description

transformations for greta arrays, which may also be used as inverse link functions. Also see operators and functions.

Usage

iprobit(x)

ilogit(x)

icloglog(x)

icauchit(x)

log1pe(x)

imultilogit(x)

Arguments

Details

greta does not allow you to state the transformation/link on the left hand side of an assignment, as is common in the BUGS and STAN modelling languages. That's because the same syntax has a very different meaning in R, and can only be applied to objects that are already in existence. The inverse forms of the common link functions (prefixed with an 'i') can be used instead.

The log1pe inverse link function is equivalent to log(1 + exp(x)), yielding a positive transformed parameter. Unlike the log transformation, this transformation is approximately linear for x > 1. i.e. when $x > 1$, $y$ is approximately $x$

imultilogit expects an n-by-m greta array, and returns an n-by-(m+1) greta array of positive reals whose rows sum to one. This is equivalent adding a final column of 0s and then running the softmax function widely used in machine learning.

Examples

## Not run: 

x1 <- normal(1, 3, dim = 10)

# transformation to the unit interval
p1 <- iprobit(x1)
p2 <- ilogit(x1)
p3 <- icloglog(x1)
p4 <- icauchit(x1)

# and to positive reals
y <- log1pe(x1)

# transform from 10x3 to 10x4, where rows are a complete set of
# probabilities
x2 <- normal(1, 3, dim = c(10, 3))
z <- imultilogit(x2)

## End(Not run)

Description

variable() creates greta arrays representing unknown parameters, to be learned during model fitting. These parameters are not associated with a probability distribution. To create a variable greta array following a specific probability distribution, see distributions().

Usage

variable(lower = -Inf, upper = Inf, dim = NULL)

cholesky_variable(dim, correlation = FALSE)

simplex_variable(dim)

ordered_variable(dim)

Arguments

Details

lower and upper must be fixed, they cannot be greta arrays. This ensures these values can always be transformed to a continuous scale to run the samplers efficiently. However, a variable parameter with dynamic limits can always be created by first defining a variable constrained between 0 and 1, and then transforming it to the required scale. See below for an example.

The constraints in simplex_variable() and ordered_variable() operate on the final dimension, which must have more than 1 element. Passing in a scalar value for dim therefore results in a row-vector.

Examples

## Not run: 

# a scalar variable
a <- variable()

# a positive length-three variable
b <- variable(lower = 0, dim = 3)

# a 2x2x2 variable bounded between 0 and 1
c <- variable(lower = 0, upper = 1, dim = c(2, 2, 2))

# create a variable, with lower and upper defined by greta arrays
min <- as_data(iris$Sepal.Length)
max <- min^2
d <- min + variable(0, 1, dim = nrow(iris)) * (max - min)

## End(Not run)
# 4x4 cholesky factor variables for covariance and correlation matrices
e_cov <- cholesky_variable(dim = 4)
e_correl <- cholesky_variable(dim = 4, correlation = TRUE)

# these can be converted to symmetic matrices with chol2symm
# (equivalent to t(e_cov) %*% e_cov, but more efficient)
cov <- chol2symm(e_cov)
correl <- chol2symm(e_correl)
# a 4D simplex (sums to 1, all values positive)
f <- simplex_variable(4)

# a 4D simplex on the final dimension
g <- simplex_variable(dim = c(2, 3, 4))
# a 2D variable with each element higher than the one in the cell to the left
h <- ordered_variable(dim = c(3, 4))

# more constraints can be added with monotonic transformations, e.g. an
# ordered positive variable
i <- exp(ordered_variable(5))

Description

This can only be run after installation has happened with install_greta_deps(), and before restarting R.

Usage

write_greta_install_log(path = greta_logfile)

Arguments

Value

nothing - writes to file