A quick-n-dirty random DAG generator

gen_rand_dag.c

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

/* http://stackoverflow.com/q/12790337/274261 */

/* Generates random DAGs. The key is to 'rank' the nodes, and
only draw edges from lower ranked nodes to higher ranked ones. */

/* Nodes/Rank: How 'fat' the DAG should be.  */
#define MIN_PER_RANK 1
#define MAX_PER_RANK 5

/* Ranks: How 'tall' the DAG should be.  */
#define MIN_RANKS 3
#define MAX_RANKS 5

/* Chance of having an Edge.  */
#define PERCENT 30

int main (void)
{
  int i, j, k, nodes = 0;
  srand (time (NULL));

  int ranks = MIN_RANKS
              + (rand () % (MAX_RANKS - MIN_RANKS + 1));

  printf ("digraph {\n");
  for (i = 0; i < ranks; i++)
    {
      /* New nodes of 'higher' rank than all nodes generated till now.  */
      int new_nodes = MIN_PER_RANK
                      + (rand () % (MAX_PER_RANK - MIN_PER_RANK + 1));

      /* Edges from old nodes ('nodes') to new ones ('new_nodes').  */
      for (j = 0; j < nodes; j++)
        for (k = 0; k < new_nodes; k++)
          if ( (rand () % 100) < PERCENT)
            printf ("  %d -> %d;\n", j, k + nodes); /* An Edge.  */

      nodes += new_nodes; /* Accumulate into old node set.  */
    }
  printf ("}\n");
  return 0;
}