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#include "cluster_finite.h"
v_t flip_cluster_finite(state_finite_t *s, v_t v0, q_t rot_ind, gsl_rng *r) {
q_t *rot = s->transformations + s->q * rot_ind;
q_t *R_inv = symmetric_invert(s->q, s->R);
v_t nv = 0;
ll_t *stack = NULL; // create a new stack
stack_push(&stack, v0); // push the initial vertex to the stack
bool *marks = (bool *)calloc(s->g->nv, sizeof(bool));
while (stack != NULL) {
v_t v = stack_pop(&stack);
if (!marks[v]) {
q_t s_old, s_new;
q_t *R_new, *R_inv_new;
bool external_flipped;
marks[v] = true;
if (v == s->g->nv - 1) {
R_new = symmetric_compose(s->q, rot, s->R);
R_inv_new = symmetric_invert(s->q, R_new);
external_flipped = true;
} else {
s_old = s->spins[v];
s_new = symmetric_act(rot, s_old);
external_flipped = false;
}
v_t nn = s->g->v_i[v + 1] - s->g->v_i[v];
for (v_t i = 0; i < nn; i++) {
q_t sn;
double prob;
bool external_neighbor = false;
v_t vn = s->g->v_adj[s->g->v_i[v] + i];
if (vn == s->g->nv - 1) {
external_neighbor = true;
} else {
sn = s->spins[vn];
}
if (external_flipped || external_neighbor) {
q_t rot_s_old, rot_s_new;
if (external_neighbor) {
rot_s_old = symmetric_act(R_inv, s_old);
rot_s_new = symmetric_act(R_inv, s_new);
} else {
rot_s_old = symmetric_act(R_inv, sn);
rot_s_new = symmetric_act(R_inv_new, sn);
}
prob = s->H_probs[rot_s_new * s->q + rot_s_old];
s->M[rot_s_old]--;
s->M[rot_s_new]++;
s->E += - s->H[rot_s_new] + s->H[rot_s_old];
} else {
q_t diff_old = (s_old + s->q - sn) % s->q;
q_t diff_new = (s_new + s->q - sn) % s->q;
prob = s->J_probs[diff_new * s->q + diff_old];
s->E += - s->J[diff_new] + s->J[diff_old];
}
if (gsl_rng_uniform(r) < prob) { // and with probability ps[e]...
stack_push(&stack, vn); // push the neighboring vertex to the stack
}
}
if (external_flipped) {
free(s->R);
free(R_inv);
s->R = R_new;
R_inv = R_inv_new;
} else {
s->spins[v] = s_new;
}
if (v != s->g->nv - 1) { // count the number of non-external sites that flip
nv++;
}
}
}
free(marks);
free(R_inv);
return nv;
}
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