subroutine fpfrno(maxtr,up,left,right,info,point,merk,n1,
* count,ier)
c subroutine fpfrno collects the free nodes (up field zero) of the
c triply linked tree the information of which is kept in the arrays
c up,left,right and info. the maximal length of the branches of the
c tree is given by n1. if no free nodes are found, the error flag
c ier is set to 1.
c ..
c ..scalar arguments..
integer maxtr,point,merk,n1,count,ier
c ..array arguments..
integer up(maxtr),left(maxtr),right(maxtr),info(maxtr)
c ..local scalars
integer i,j,k,l,n,niveau
c ..
ier = 1
if(n1.eq.2) go to 140
niveau = 1
count = 2
10 j = 0
i = 1
20 if(j.eq.niveau) go to 30
k = 0
l = left(i)
if(l.eq.0) go to 110
i = l
j = j+1
go to 20
30 if(i-count) 110,100,40
40 if(up(count).eq.0) go to 50
count = count+1
go to 30
50 up(count) = up(i)
left(count) = left(i)
right(count) = right(i)
info(count) = info(i)
if(merk.eq.i) merk = count
if(point.eq.i) point = count
if(k.eq.0) go to 60
right(k) = count
go to 70
60 n = up(i)
left(n) = count
70 l = left(i)
80 if(l.eq.0) go to 90
up(l) = count
l = right(l)
go to 80
90 up(i) = 0
i = count
100 count = count+1
110 l = right(i)
k = i
if(l.eq.0) go to 120
i = l
go to 20
120 l = up(i)
j = j-1
if(j.eq.0) go to 130
i = l
go to 110
130 niveau = niveau+1
if(niveau.le.n1) go to 10
if(count.gt.maxtr) go to 140
ier = 0
140 return
end