pretrain: Pre-trains the DeepBeliefNet or RestrictedBolzmannMachine

In xrobin/DeepLearning: Deep Learning of neural networks

Description

A contrastive divergence method is used to train each layer sequentially.

Usage

pretrain(x, data, ...)

## S3 method for class 'RestrictedBolzmannMachine'
pretrain(x, data, miniters = 100,
  maxiters = floor(dim(data)[1]/batchsize), batchsize = 100, momentum = 0,
  penalization = c("l1", "l2", "none"), lambda = 0, lambda.b = lambda,
  lambda.c = lambda, lambda.W = lambda, epsilon = ifelse(x$output$type ==
  "gaussian", 0.001, 0.1), epsilon.b = epsilon, epsilon.c = epsilon,
  epsilon.W = epsilon, train.b = TRUE, train.c = TRUE,
  continue.function = continue.function.exponential,
  continue.function.frequency = 1000, continue.stop.limit = 30,
  diag = list(rate = diag.rate, data = diag.data, f = diag.function),
  diag.rate = c("none", "each", "accelerate"), diag.data = NULL,
  diag.function = NULL, n.proc = detectCores() - 1, ...)

## S3 method for class 'DeepBeliefNet'
pretrain(x, data, miniters = 100,
  maxiters = floor(dim(data)[1]/batchsize), batchsize = 100,
  skip = numeric(0), momentum = 0, penalization = "l1", lambda = 2e-04,
  lambda.b = lambda, lambda.c = lambda, lambda.W = lambda,
  epsilon = 0.1, epsilon.b = epsilon, epsilon.c = epsilon,
  epsilon.W = epsilon, train.b = TRUE, train.c = length(x) - 1,
  continue.function = continue.function.exponential,
  continue.function.frequency = 100, continue.stop.limit = 3,
  diag = list(rate = diag.rate, data = diag.data, f = diag.function),
  diag.rate = c("none", "each", "accelerate"), diag.data = NULL,
  diag.function = NULL, n.proc = detectCores() - 1, ...)

pretrain.progress

Arguments

x	the DeepBeliefNet or RestrictedBolzmannMachine object
data	the dataset, either as matrix or data.frame. The number of columns must match the number of nodes of the network input
...	ignored
miniters, maxiters	minimum and maximum number of iterations to perform
batchsize	the size of the minibatches
momentum	the momentum, between 0 (no momentum) and 1 (no training). See the Momentums section below.
penalization	the penalization mode. Either “l1” (sparse), “l2” (quadratic) or “none”.
lambda	penalty on large weights (weight-decay). Alternatively one can define lambda.b, lambda.c and lambda.W to constrain bs, cs and Ws, respectively. Default: 0 = no penalization (equivalent to penalization="none").
lambda.b, lambda.c, lambda.W	separate penalty rates for bs, cs and Ws. Take precedence over lambda.
epsilon	learning rate. Alternatively one can define epsilon.b, epsilon.c and epsilon.W (see below) to learn bs, cs and Ws, respectively, at different speeds. Defaut: 0.1 (for layers where all inputs and outputs are binary or continuous) or 0.001 (for layers with gaussian input or output).
epsilon.b, epsilon.c, epsilon.W	separate learning rates for bs, cs and Ws. Take precedence over epsilon.
train.b, train.c	whether (RestrictedBolzmannMachine) or on which layers (DeepBeliefNet) to update the bs and cs. For a RestrictedBolzmannMachine, must be a logical of length 1. For a DeepBeliefNet must be a logical (can be recycled) or numeric index of layers.
continue.function	that can stop the pre-training between miniters and maxiters if it returns FALSE. By default, continue.function.exponential will be used. An alternative is to use continue.function.always that will always return true and thus carry on with the training until maxiters is reached. A user-supplied function must accept (error, iter, batchsize) as input and return a logical of length 1. The training is stopped when it returns FALSE.
continue.function.frequency	the frequency at which continue.function will be assessed.
continue.stop.limit	the number of consecutive times continue.function must return FALSE before the training is stopped. For example, 1 will stop as soon as continue.function returns FALSE, whereas Inf will ensure the result of continue.function is never enforced (but the function is still executed). The default is 3 so the training will continue until 3 consecutive calls of continue.function returned FALSE, giving more robustness to the decision.
diag, diag.rate, diag.data, diag.function	diagnostic specifications. See details.
n.proc	number of cores to be used for Eigen computations
skip	numeric vector of the RestrictedBolzmannMachine of the DeepBeliefNet to be skipped.

Format

An object of class list of length 3.

Value

pre-trained object with the pretrained switch set to TRUE.

Pretraining Layers of the Deep Belief Net with Different Parameters

It is possible to pre-train the layers of a DeepBeliefNet with different parameters. The following parameters can be supplied as vectors with length of the network - 1: batchsize, penalization, labmda, lambda.b, lambda.c, lambda.W, epsilon, epsilon.b, epsilon.c and epsilon.W. The values will be recycled if necessary (with essentially no warning if the lengths doesn't match). The special case of the momentum parameters is described below.

Momentums

The momentum parameter can take several length, and will be interpreted accordingly:

• 1: constant momentum

• 2: a gradient, will be interpreted as seq(momentum[1], momentum[2], length.out=maxiters)

• maxiter: encodes the momentum per iteration

To specify different momentums for the different layers of a DeepBeliefNet, they must be passed as a list of the same length than the number of RestrictedBolzmannMachines to pretrain, and they will be interpreted per layer as described above.

Diagnostic specifications

The specifications can be passed directly in a list with elements rate, data and f, or separately with parameters diag.rate, diag.data and diag.function. The function must be of the following form: function(rbm, batch, data, iter, batchsize, maxiters, layer)

• rbm: the RBM object after the training iteration.

• batch: the batch that was used at that iteration.

• data: the data provided in diag.data or diag$data, possibly transformed through the previous layers of the DBN.

• iter: the training iteration number, starting from 0 (before the first iteration).

• batchsize: the size of the batch.

• maxiters: the target number of iterations.

• layer: the layer number, starting from 0.

The following diag.rate or diag$rate are supported:

• “none”: the diag function will never be called.

• “each”: the diag function will be called before the first iteration, and at the end of each iteration.

• “accelerate”: the diag function will called before the first iteration, at the first 200 iterations, and then with a rate slowing down proportionally with the iteration number. It is always called at the last iteration.

Note that diag functions incur a slight overhead as they involve a callback to R and multiple object conversions. Setting diag.rate = "none" removes any overhead.

Progress

pretrain.progress is a convenient pre-built diagnostic specification that displays a progress bar per training layer.

Examples

library(mnist)
data(mnist)
# Initialize a 784-1000-500-250-30 layers DBN to process the MNIST data set
dbn.mnist <- DeepBeliefNet(Layers(c(784, 1000, 500, 250, 30), input="continuous", output="gaussian"))
print(dbn.mnist)

## Not run: 
# Pre-train this DBN
pretrained.mnist <- pretrain(dbn.mnist, mnist$train$x, 
								 penalization = "l2", lambda=0.0002, epsilon=c(.1, .1, .1, .001), 
								 batchsize = 100, maxiters=1000000)

## End(Not run)

## Not run: 
# Pretrain with a progress bar
# In this case the overhead is around 1%
diag <- list(rate = "accelerate", data = NULL, f = function(rbm, batch, data, iter, batchsize, maxiters, layer) {
	if (iter == 0) {
		DBNprogressBar <<- txtProgressBar(min = 0, max = maxiters, initial = 0, width = NA, style = 3)
	}
	else if (iter == maxiters) {
		setTxtProgressBar(DBNprogressBar, iter)
		close(DBNprogressBar)
	}
	else {
		setTxtProgressBar(DBNprogressBar, iter)
	}
})
pretrained.mnist <- pretrain(dbn.mnist, mnist$train$x,  penalization = "l2", lambda=0.0002,
                             epsilon=c(.1, .1, .1, .001), batchsize = 100, maxiters=1e4,
                             continue.function = continue.function.always, diag = diag)
# Equivalent to using pretrain.progress
pretrained.mnist <- pretrain(dbn.mnist, mnist$train$x,  penalization = "l2", lambda=0.0002,
                             epsilon=c(.1, .1, .1, .001), batchsize = 100, maxiters=1e4,
                             continue.function = continue.function.always, diag = pretrain.progress)

## End(Not run)

xrobin/DeepLearning documentation built on May 17, 2018, 3:51 a.m.