/*************************************************************************
* This file randomly permutes the contents of an array.
* flag == 0, don't initialize perm
* flag == 1, set p[i] = i
**************************************************************************/
void gk_RandomPermute(size_t n, int *p, int flag)
{
size_t i, u, v;
int tmp;
if (flag == 1) {
for (i=0; i<n; i++)
p[i] = i;
}
for (i=0; i<n/2; i++) {
v = RandomInRange(n);
u = RandomInRange(n);
gk_SWAP(p[v], p[u], tmp);
}
}
int gk_rw_PageRank(gk_csr_t *mat, float lamda, float eps, int max_niter, float *pr)
{
ssize_t i, j, iter, nrows;
double *rscale, *prold, *prnew, *prtmp;
double fromsinks, error;
ssize_t *rowptr;
int *rowind;
float *rowval;
nrows = mat->nrows;
rowptr = mat->rowptr;
rowind = mat->rowind;
rowval = mat->rowval;
prold = gk_dsmalloc(nrows, 0, "gk_rw_PageRank: prnew");
prnew = gk_dsmalloc(nrows, 0, "gk_rw_PageRank: prold");
rscale = gk_dsmalloc(nrows, 0, "gk_rw_PageRank: rscale");
/* compute the scaling factors to get adjacency weights into transition
probabilities */
for (i=0; i<nrows; i++) {
for (j=rowptr[i]; j<rowptr[i+1]; j++)
rscale[i] += rowval[j];
if (rscale[i] > 0)
rscale[i] = 1.0/rscale[i];
}
/* the restart distribution is the initial pr scores */
for (i=0; i<nrows; i++)
prnew[i] = pr[i];
/* get into the PR iteration */
for (iter=0; iter<max_niter; iter++) {
gk_SWAP(prnew, prold, prtmp);
gk_dset(nrows, 0.0, prnew);
/* determine the total current PR score of the sinks so that you
can distribute them to all nodes according to the restart
distribution. */
for (fromsinks=0.0, i=0; i<nrows; i++) {
if (rscale[i] == 0)
fromsinks += prold[i];
}
/* push random-walk scores to the outlinks */
for (i=0; i<nrows; i++) {
for (j=rowptr[i]; j<rowptr[i+1]; j++)
prnew[rowind[j]] += prold[i]*rscale[i]*rowval[j];
}
/* apply the restart conditions */
for (i=0; i<nrows; i++) {
prnew[i] = lamda*(fromsinks*pr[i]+prnew[i]) + (1.0-lamda)*pr[i];
}
/* compute the error */
for (error=0.0, i=0; i<nrows; i++)
error = (fabs(prnew[i]-prold[i]) > error ? fabs(prnew[i]-prold[i]) : error);
//printf("nrm1: %le maxfabserr: %le\n", gk_dsum(nrows, prnew, 1), error);
if (error < eps)
break;
}
/* store the computed pr scores into pr for output */
for (i=0; i<nrows; i++)
pr[i] = prnew[i];
gk_free((void **)&prnew, &prold, &rscale, LTERM);
return (int)(iter+1);
}
