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## cycletest.R
## Author : Claus Dethlefsen
## Created On : Fri Dec 21 14:04:58 2001
## Last Modified By: Claus Dethlefsen
## Last Modified On: Sun Sep 15 08:05:24 2002
## Update Count : 59
## Status : Unknown, Use with caution!
###############################################################################
##
## Copyright (C) 2002 Susanne Gammelgaard Bottcher, Claus Dethlefsen
##
## 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 2 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, write to the Free Software
## Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
######################################################################
cycletest <- function(nw) {
## Does nw contain a cycle?
##
## Algorithm:
## if nw$n == 1 return(F)
## else res <- findleaf(nw) ## res=0 if no leaf else idx of leaf
## if res==0 return(T)
## else nw <- (nw with node idx deleted)
## cycletest(nw)
##
## Uses: findleaf
## and network attributes:
## n,nodes
## Used by: networkfamily, drawnetwork, autosearch,
## addrandomarrow, turnrandomarrow
if (nw$n == 1) { #cat("only one node\n");
return(FALSE)}
else {
res <- findleaf(nw)
if (res == 0) {
## cat("No leaf found\n");
return(TRUE)
}
else {
## cat("deleting node: ",nw$nodes[[res]]$name,"\n")
nw$nodes <- nw$nodes[-res]
nw$n <- nw$n - 1
## should update cont and disc, but I won't. Just be careful
## how you use the procedure!
cycletest(nw)
}
}
}
findleaf <- function(nw) {
## find a node not being a parent to any other node
##
## Uses network attributes: n, nodes
## and node attributes: idx, parents
##
## Used by: cycletest
jump <- FALSE
for (i in 1:nw$n) { ## for each node
for (j in 1:nw$n) { ## testing i against i (hmm)
## cat("Is",nw$nodes[[i]]$name,"parent to",nw$nodes[[j]]$name,"?")
## is i a parent to j?
## Here, it is necessary to use 'idx', since we have been
## deleting nodes. Thus the indices are no longer 1:n
res <- match(nw$nodes[[i]]$idx, nw$nodes[[j]]$parents)
if (!is.na(res)) { ## i is not a leaf
jump <- TRUE
break ## next i
}
}
if (!jump) return(i)
jump <- FALSE
}
## did not find any
res <- 0
res
}
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