# R/crossentropy.R In rinform: An R Wrapper of the 'Inform' C Library for Information Analysis of Complex Systems

#### Documented in cross_entropy

```################################################################################
# Copyright 2017-2018 Gabriele Valentini, Douglas G. Moore. All rights reserved.
# Use of this source code is governed by a MIT license that can be found in the
# LICENSE file.
################################################################################

################################################################################
#' Cross Entropy
#'
#' Compute the cross entropy between the "true" and "unnatural" distributions
#' \code{p} and \code{q} from associated time series \code{ps} and \code{qs},
#' respectively. Cross entropyâ€™s local variant is equivalent to the
#' self-information of \code{q}, and as such is implemented by the local block
#' entropy.
#'
#' @param ps Vector specifying a time series drawn from
#'        the true distribution.
#' @param qs Vector specifying a time series drawn from
#'        the unnatural distribution.
#'
#' @return Numeric giving the cross entropy.
#'
#' @example inst/examples/ex_crossentropy.R
#'
#' @export
#'
#' @useDynLib rinform r_cross_entropy_
################################################################################
cross_entropy <- function(ps, qs) {
n   <- 0
ce  <- 0
err <- 0

.check_series(ps)
.check_series(qs)
.check_series_vector(ps)
.check_series_vector(qs)

# Extract number of series and length
if (length(ps) != length(qs)) {
stop("<", deparse(substitute(ps)), "> and <", deparse(substitute(qs)), "> differ in length")
}
n <- length(qs)

# Convert to integer vector suitable for C
ps <- as.integer(ps)
qs <- as.integer(qs)

# Compute the value of <b>
b <- max(2, max(ps) + 1, max(qs) + 1)

x <- .C("r_cross_entropy_",
ps      = as.integer(ps),
qs      = as.integer(qs),
n       = as.integer(n),
b       = as.integer(b),
rval    = as.double(ce),
err     = as.integer(err))

if (.check_inform_error(x\$err) == 0) {
ce <- x\$rval
}

ce
}
```

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rinform documentation built on April 1, 2018, 12:12 p.m.