subroutine pred(kpr,i,j,nadj,madj,ntot)

# Find the predecessor of j in the adjacency list of i.
# Called by initad, trifnd, swap, dirseg, dirout.

implicit double precision(a-h,o-z)
dimension nadj(-3:ntot,0:madj)
dimension ndi(1)

# Set dummy integer for call to intpr(...).
ndi(1) = 0

n = nadj(i,0)

# If the adjacency list of i is empty, then clearly j has no predecessor
# in this adjacency list. Something's wrong; stop.
if(n==0) {
    call intpr("Adjacency list of i is empty, and so cannot contain j.",-1,ndi,0)
    call rexit("Bailing out of pred.")
}

# The adjacency list of i is non-empty; search through it until j is found;
# subtract 1 from the location of j, and find the contents of this new location
do k = 1,n {
    if(j==nadj(i,k)) {
        km = k-1
        if(km<1) km = n         # Take km modulo n. (The adjacency list
        kpr = nadj(i,km)        # is circular.)
        return
    }
}

# The adjacency list for i doesn't contain j.  Something's wrong; stop.
    call intpr("Adjacency list of i does not contain j.",-1,ndi,0)
    call rexit("Bailing out of pred.")
end