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/*************************************************************************
* Copyright (c) 2011 AT&T Intellectual Property
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* https://www.eclipse.org/legal/epl-v10.html
*
* Contributors: Details at https://graphviz.org
*************************************************************************/
#include <neatogen/digcola.h>
#include <util/alloc.h>
#ifdef DIGCOLA
#include <neatogen/kkutils.h>
/*
* This function partitions the graph nodes into levels
* according to the minimizer of the hierarchy energy.
*
* To allow more flexibility we define a new level only
* when the hierarchy energy shows a significant jump
* (to compensate for noise).
* This is controlled by two parameters: 'abs_tol' and
* 'relative_tol'. The smaller these two are, the more
* levels we'll get.
* More specifically:
* We never consider gaps smaller than 'abs_tol'
* Additionally, we never consider gaps smaller than 'abs_tol'*<avg_gap>
*
* The output is an ordering of the nodes according to
* their levels, as follows:
* First level:
* ordering[0],ordering[1],...ordering[levels[0]-1]
* Second level:
* ordering[levels[0]],ordering[levels[0]+1],...ordering[levels[1]-1]
* ...
* Last level:
* ordering[levels[num_levels-1]],ordering[levels[num_levels-1]+1],...ordering[n-1]
*
* Hence, the nodes were partitioned into 'num_levels'+1
* levels.
*
* Please note that 'ordering[levels[i]]' contains the first node at level i+1,
* and not the last node of level i.
*/
int
compute_hierarchy(vtx_data * graph, int n, double abs_tol,
double relative_tol, double *given_coords,
int **orderingp, int **levelsp, int *num_levelsp)
{
double *y;
int i, rv=0;
int *ordering;
int *levels;
double tol; /* node 'i' precedes 'j' in hierarchy iff y[i]-y[j]>tol */
double hierarchy_span;
int num_levels;
/* compute optimizer of hierarchy energy: 'y' */
if (given_coords) {
y = given_coords;
} else {
y = gv_calloc(n, sizeof(double));
if (compute_y_coords(graph, n, y, n)) {
rv = 1;
goto finish;
}
}
// sort nodes according to their y-ordering
*orderingp = ordering = gv_calloc(n, sizeof(int));
for (i = 0; i < n; i++) {
ordering[i] = i;
}
quicksort_place(y, ordering, n);
/* compute tolerance
* take the maximum between 'abs_tol' and a fraction of the average gap
* controlled by 'relative_tol'
*/
hierarchy_span = y[ordering[n - 1]] - y[ordering[0]];
tol = MAX(abs_tol, relative_tol * hierarchy_span / (n - 1));
/* 'hierarchy_span/(n-1)' - average gap between consecutive nodes */
/* count how many levels the hierarchy contains (a SINGLE_LINK clustering */
/* alternatively we could use COMPLETE_LINK clustering) */
num_levels = 0;
for (i = 1; i < n; i++) {
if (y[ordering[i]] - y[ordering[i - 1]] > tol) {
num_levels++;
}
}
*num_levelsp = num_levels;
if (num_levels == 0) {
*levelsp = levels = gv_calloc(1, sizeof(int));
levels[0] = n;
} else {
int count = 0;
*levelsp = levels = gv_calloc(num_levels, sizeof(int));
for (i = 1; i < n; i++) {
if (y[ordering[i]] - y[ordering[i - 1]] > tol) {
levels[count++] = i;
}
}
}
finish:
if (!given_coords) {
free(y);
}
return rv;
}
#endif /* DIGCOLA */
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