function(aa = 100, dd = 20, tt = 50)
{
#program initilize()
#
#Initializes global variables (hard assignment used throughout). With the
#exception of the upper limits of the age (a), duration (d) and time (t)
#indices and the corresponding label vectors, all values are set to zero.
#This function serves only to set array dimensions, input values are
#written to these arrays using the various input utility programs.
#
#preparatory
#
	aa <<- aa	#           #upper limit of age index
	dd <<- dd	#           #pper limit of duration index
	tt <<- tt	#           #upper limit of time index
	ages <<- 0:(aa - 1)	#   #age labels
	durations <<- 0:(dd - 1)	#duration labels
	times <<- 0:(tt - 1)	#   #time labels
#
#   #1, 2 and 3 dimensional dummy arrays
#
	dummy1 <- rep(0, times = tt)
	names(dummy1) <- 0:(tt - 1)
	dummy2 <- array(data = 0, dim = c(aa, tt), dimnames = list(ages, times))
	dummy3 <- array(data = 0, dim = c(aa, dd, tt), dimnames = list(ages, durations, times))	#
#
#population state arrays (x=inactive, y=active,uninfected, z=infected, f=female, m=male)
#
	xm <<- xf <<- dummy2	#inactive males and females
	ym <<- yf <<- dummy2	#active, uninfected males and females
	zm <<- zf <<- dummy3	#infected males and females
#
#birth rates (beta), proportions of female and male births (sigma), 
#vertical transmission (zeta)
#
	beta.y <<- beta.z <<- dummy2	#birth rates for active-uninfected and infected
	sigma.m <<- sigma.f <<- 0.5	#   #proportions of females and males among all births
	zeta <<- rep(0, times = tt)	#   #vertical transmission proportion
#
#forces; initialize mu.f and mu.m to small positive values to avoid zero denominators
#in multiple decrement expressions.
#
	mu.f <<- mu.m <<- dummy2	#       #force of mortality from non-HIV-related causes
	mu.fb <<- mu.mb <<- dummy1	#       #force of non-HIV-related mortality for births    
	upsilon.m <<- upsilon.f <<- dummy2	#force of becoming active
	tau.m <<- tau.f <<- dummy2	#       #force of becoming inactive
	lamda.m <<- lamda.f <<- dummy2	#   #force of becoming infected
	alpha <<- dummy3	#               #force of dying from HIV-related causes
	alpha.b <<- dummy1	#               #force of HIV-related mortality for infected births
#
#force of infection parameters (see text for explanation)
#    
	iota.f <<- iota.m <<- dummy2	#additive lamda parameter
	kappa.f <<- kappa.m <<- dummy1	#time independent multiplicative lamda parameter
	theta.f <<- theta.m <<- dummy2	#time dependent multiplicative lamda parameter
#
#flow arrays (xd=inactive to dead, xy=inactive to active, yx=active to inactive, etc.)
#
	xdm <<- xdf <<- dummy2	#   #deaths of inactive persons
	xym <<- xyf <<- dummy2	#   #movements of inactive persons to active status
	yxm <<- yxf <<- dummy2	#   #movements of active persons to inactive status
	yzm <<- yzf <<- dummy2	#   #movements of active persons to infected status
	ydm <<- ydf <<- dummy2	#   #deaths of active persons
	zdm <<- zdf <<- dummy3	#   #deaths of infected persons from non-HIV-related causes
	zam <<- zaf <<- dummy3	#   #deaths of infected persons from HIV-related causes
	ubf <<- ubm <<- dummy1	#   #uninfected births
	ubdm <<- ubdf <<- dummy1	#deaths of uninfected births
	ibf <<- ibm <<- dummy1	#   #infected births
	ibdm <<- ibdf <<- dummy1	#non-HIV-related deaths of infected births
	ibam <<- ibaf <<- dummy1	#HIV-related deaths of infected births
#
	write.ascii(initialize)
	"All done"
}