void derivatives()
{
Graph *graph = sub->subgraph;
for (unsigned k = 0; k < pnum; k++)
{
unsigned iter = 0;
bool stop = false;
// We are done when maxiteration is reached
// or the error is small enough.
while (iter < maxiter && !stop)
{
iter++;
// copy last iteration
#pragma omp parallel for
for (unsigned i = 0; i < nvert; i++)
{
dlast[i][k] = deriv[i][k];
deriv[i][k] = 0.0;
}
#pragma omp parallel for
for (unsigned id = 0; id < nvert; id++)
{
for (Graph::iterator e = graph->iterate_outgoing_edges(id); !e.end(); e++)
{
user_id fr = (*e).v2;
double calc = sub->score(id, fr) * dlast[id][k]
+
pagerank[id] * (1.0-alpha) * params->qderiv(id, fr, k);
#pragma omp atomic
deriv[fr][k] += calc;
}
}
stop = true;
for (unsigned d = 0; d < sub->positive.size(); d++)
{
unsigned pos = sub->positive[d];
if (fabs(deriv[pos][k] - dlast[pos][k]) > tolerance)
stop = false;
}
for (unsigned l = 0; l < sub->negative.size(); l++)
{
unsigned neg = sub->negative[l];
if (fabs(deriv[neg][k] - dlast[neg][k]) > tolerance)
stop = false;
}
}
cout << "Derivative iterations: " << iter << endl;
}
}
// Personalized pagerank starting from vertex start (at index 0)
void pers_pagerank()
{
Graph *graph = sub->subgraph;
unsigned iter = 0;
double err = 1.0;
// We are done when maxiteration is reached
// or the error is small enough.
while (iter++ < maxiter && err > tolerance)
{
// copy last iteration to last array
// and clear pagerank array
#pragma omp parallel for
for (unsigned i = 0; i < nvert; i++)
{
last[i] = pagerank[i];
pagerank[i] = 0.0;
}
// sum up the nodes without outgoing edges ("dangling nodes").
// their pagerank sum will be uniformly distributed among all nodes.
double zsum = 0.0;
#pragma omp parallel for reduction(+:zsum)
for (unsigned i = 0; i < sub->zerodeg.size(); i++)
zsum += last[ sub->zerodeg[i] ];
double nolinks = (1.0-alpha) * zsum / nvert;
pagerank[0] += alpha; // add teleport probability to the start vertex
#pragma omp parallel for
for (unsigned id = 0; id < nvert; id++)
{
double update = (1.0-alpha) * last[id];
for (Graph::iterator e = graph->iterate_outgoing_edges(id); !e.end(); e++)
{
#pragma omp atomic
pagerank[(*e).v2] += (update * sub->score(id, (*e).v2));
}
#pragma omp atomic
pagerank[id] += nolinks; // pagerank from "dangling nodes"
}
// sum the pagerank
double sum = 0.0;
#pragma omp parallel for reduction(+:sum)
for (unsigned i = 0; i < nvert; i++)
sum += pagerank[i];
// normalize to valid probabilities, from 0 to 1.
sum = 1.0 / sum;
#pragma omp parallel for
for (unsigned i = 0; i < nvert; i++)
pagerank[i] *= sum;
// sum up the error
err = 0.0;
#pragma omp parallel for reduction(+:err)
for (unsigned i = 0; i < nvert; i++)
err += fabs(pagerank[i] - last[i]);
//cout << "Iteration " << iter << endl;
//cout << "Error: " << err << endl;
}
//cout << "PageRank iterations: " << iter << endl;
}
