acs<-function(execesses){

# Compute average cluster size for a given three-dimensional array of excesses
#
#  Description:
#
#       Returns average cluster size 
#
# Usage: acs(execesses)
#
# Input:
#
#       excesses: p (space) x q (space) x n (time) array of excesses
#
# Output:
#
#       A p x q matrix containing the average cluster size
#
# Authors:
#
#      Caio Coelho <c.a.d.s.coelho@reading.ac.uk> 28 Feb 2006
#      Chris Ferro <c.a.t.ferro@reading.ac.uk>



avenumbexceed<-function(y){
  x<-matrix(y,ncol=3,nrow=length(y)/3,byrow=T)
  sum(x > 0,na.rm=T) / sum(apply(x > 0, 1, any,na.rm=T),na.rm=T)
}

apply(execesses,c(1,2),avenumbexceed)

}