# sos2tf.R
# Copyright (C) 2020 Geert van Boxtel <gjmvanboxtel@gmail.com>
# Original Octave version:
# Copyright (C) 2005 Julius O. Smith III <jos@ccrma.stanford.edu>
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version 3
# of the License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
#
# Version history
# 20200330 GvB setup for gsignal v0.1.0
# 20200406 GvB validated
# 20210306 GvB initialize a, b with sos[1, ] instead of 1 (bug in Octave
# signal?)
# 20210326 GvB return object of class 'Arma'
# 20210506 GvB use matrix() instead of as.matrix()
#------------------------------------------------------------------------------
#' Sos to transfer function
#'
#' Convert digital filter second-order section data to transfer function form.
#'
#' @param sos Second-order section representation, specified as an nrow-by-6
#' matrix, whose rows contain the numerator and denominator coefficients of
#' the second-order sections:\cr \code{sos <- rbind(cbind(B1, A1), cbind(...),
#' cbind(Bn, An))}, where \code{B1 <- c(b0, b1, b2)}, and \code{A1 <- c(a0,
#' a1, a2)} for section 1, etc. The b0 entry must be nonzero for each section.
#' @param g Overall gain factor that effectively scales the output \code{b}
#' vector (or any one of the input \code{Bi} vectors). Default: 1.
#'
#' @return An object of class "Arma" with the following list elements:
#' \describe{
#' \item{b}{moving average (MA) polynomial coefficients}
#' \item{a}{autoregressive (AR) polynomial coefficients}
#' }
#'
#' @seealso \code{\link{as.Arma}}, \code{\link{filter}}
#'
#' @examples
#' sos <- rbind(c(1, 1, 1, 1, 0, -1), c(-2, 3, 1, 1, 10, 1))
#' ba <- sos2tf(sos)
#'
#' @author Julius O. Smith III, \email{jos@@ccrma.stanford.edu}.\cr
#' Conversion to R by Geert van Boxtel, \email{gjmvanboxtel@@gmail.com}.
#'
#' @export
sos2tf <- function(sos, g = 1) {
sos <- matrix(sos, ncol = 6)
n <- nrow(sos)
m <- ncol(sos)
if (n <= 0) {
stop("sos must have at least 1 row")
}
if (m != 6) {
stop("sos must be a nrow-by-6 matrix")
}
b <- sos[1, 1:3]
a <- sos[1, 4:6]
if (n > 1) {
for (i in 2:n) {
b <- conv(b, sos[i, 1:3])
a <- conv(a, sos[i, 4:6])
}
}
nb <- length(b)
while (nb > 0 && b[nb] == 0) {
b <- b[1:(nb - 1)]
nb <- length(b)
}
na <- length(a)
while (na > 0 && a[na] == 0) {
a <- a[1:(na - 1)]
na <- length(a)
}
b <- b * prod(g)
Arma(b = b, a = a)
}
Add the following code to your website.
For more information on customizing the embed code, read Embedding Snippets.