static inline const typename Tensor::elt_t
do_expected12(const iTEBD<Tensor> &psi, const Tensor &Op12, int site)
{
if (!psi.is_canonical()) {
return do_expected12(psi.canonical_form(), Op12, site);
} else {
tensor::index a, i, b, j;
const Tensor &AlA = psi.combined_matrix(0);
const Tensor &BlB = psi.combined_matrix(1);
AlA.get_dimensions(&a, &i, &b);
BlB.get_dimensions(&b, &j, &a);
Tensor v1 = psi.left_boundary(0);
Tensor v2 = v1;
if (site & 1) {
v1 = propagate_right(v1, AlA);
v2 = v1;
const Tensor BlBAlA = reshape(fold(BlB, -1, AlA, 0), b, j*i, b);
v1 = propagate_right(v1, BlBAlA, Op12);
v2 = propagate_right(v2, BlBAlA);
v1 = propagate_right(v1, BlB);
v2 = propagate_right(v2, BlB);
} else {
const Tensor AlABlB = reshape(fold(AlA, -1, BlB, 0), a, i*j, a);
v1 = propagate_right(v1, AlABlB, Op12);
v2 = propagate_right(v2, AlABlB);
}
return trace(v1) / trace(v2);
}
}
static inline const typename Tensor::elt_t
do_string_order(const iTEBD<Tensor> &psi,
const Tensor &Opi, int i, const Tensor &Opmiddle,
const Tensor &Opj, int j)
{
if (i == j) {
return expected(psi, mmult(Opi, Opj), i);
} else if (i > j) {
return do_string_order(psi, Opj, j, Opmiddle, Opi, i);
} else if (!psi.is_canonical()) {
return do_string_order(psi.canonical_form(), Opi, i, Opmiddle, Opj, j);
} else {
j = j - i;
i = i & 1;
j = j + i;
Tensor v1 = psi.left_boundary(0);
Tensor v2 = v1;
const Tensor none;
const Tensor *op;
for (int site = 0; (site <= j) || !(site & 1); ++site) {
if (site == i)
op = &Opi;
else if (site == j)
op = &Opj;
else if (site > i && site < j)
op = &Opmiddle;
else
op = &none;
v1 = propagate_right(v1, psi.combined_matrix(site), *op);
v2 = propagate_right(v2, psi.combined_matrix(site));
}
return trace(v1) / trace(v2);
}
}
static inline const Tensor
do_string_order_many(const iTEBD<Tensor> &psi,
const Tensor &Opi, const Tensor &Opmiddle,
const Tensor &Opj, int N)
{
if (!psi.is_canonical()) {
return do_string_order_many(psi.canonical_form(), Opi, Opmiddle, Opj, N);
} else {
Tensor v1 = psi.left_boundary(0);
Tensor v2 = v1;
Tensor output(N);
Tensor nextv2;
for (int site = 0; (site < N); ++site) {
const Tensor &aux = psi.combined_matrix(site);
Tensor v = propagate_right(v1, aux, site? Opj : mmult(Opi,Opj));
if (nextv2.size()) {
v2 = nextv2;
} else {
v2 = propagate_right(v2, aux);
}
if (!(site & 1)) {
const Tensor &aux = psi.combined_matrix(site+1);
nextv2 = propagate_right(v2, aux);
v = propagate_right(v, aux);
output.at(site) = trace(v) / trace(nextv2);
} else {
nextv2 = Tensor();
output.at(site) = trace(v) / trace(v2);
}
if (site) {
v1 = propagate_right(v1, aux, Opmiddle);
} else {
v1 = propagate_right(v1, aux, Opi);
}
}
return output;
}
}
const iTEBD<Tensor>
evolve_itime(iTEBD<Tensor> psi, const Tensor &H12,
double dt, tensor::index nsteps,
double tolerance, tensor::index max_dim,
tensor::index deltan, int method,
std::vector<double> *energies,
std::vector<double> *entropies)
{
static const double FR_param[5] =
{0.67560359597983, 1.35120719195966, -0.17560359597983, -1.70241438391932};
Tensor eH12[4];
//int method = 2;
switch (method) {
case 1:
/* Second order Trotter expansion */
eH12[1] = linalg::expm((-dt/2) * H12);
case 0:
/* First order Trotter expansion */
eH12[0] = linalg::expm((-dt) * H12);
break;
default:
/* Fourth order Trotter expansion */
for (int i = 0; i < 4; i++) {
eH12[i] = linalg::expm((-dt*FR_param[i]) * H12);
}
}
Tensor Id = Tensor::eye(H12.rows());
double time = 0;
psi = psi.canonical_form();
double E = energy(psi, H12), S = psi.entropy();
if (energies)
energies->push_back(E);
if (entropies)
entropies->push_back(S);
if (!deltan) {
deltan = 1;
}
std::cout.precision(5);
std::cout << nsteps << ", " << dt << " x " << deltan
<< " = " << dt * deltan << std::endl;
std::cout << "t=" << time
<< ";\tE=" << E << "; dE=" << 0.0
<< ";\tS=" << S << "; dS=" << 0.0
<< ";\tl=" << std::max(psi.left_dimension(0),
psi.right_dimension(0))
<< std::endl
<< "l = " << matrix_form(real(psi.left_vector(0)))
<< std::endl;
for (size_t phases = (nsteps + deltan - 1) / deltan; phases; phases--) {
for (size_t i = 0; (i < deltan); i++) {
switch (method) {
case 0:
psi = psi.apply_operator(eH12[0], 0, tolerance, max_dim);
psi = psi.apply_operator(eH12[0], 1, tolerance, max_dim);
break;
case 1:
psi = psi.apply_operator(eH12[1], 0, tolerance, max_dim);
psi = psi.apply_operator(eH12[0], 1, tolerance, max_dim);
psi = psi.apply_operator(eH12[1], 0, tolerance, max_dim);
break;
default:
psi = psi.apply_operator(eH12[0], 0, tolerance, max_dim);
psi = psi.apply_operator(eH12[1], 1, tolerance, max_dim);
psi = psi.apply_operator(eH12[2], 0, tolerance, max_dim);
psi = psi.apply_operator(eH12[3], 1, tolerance, max_dim);
psi = psi.apply_operator(eH12[2], 0, tolerance, max_dim);
psi = psi.apply_operator(eH12[1], 1, tolerance, max_dim);
psi = psi.apply_operator(eH12[0], 0, tolerance, max_dim);
}
time += dt;
}
psi = psi.canonical_form();
double newE = energy(psi, H12);
double newS = psi.entropy();
if (energies)
energies->push_back(newE);
if (entropies)
entropies->push_back(newS);
std::cout << "t=" << time
<< ";\tE=" << newE << "; dE=" << newE-E
<< ";\tS=" << newS << "; dS=" << newS-S
<< ";\tl=" << std::max(psi.left_dimension(0),
psi.right_dimension(0))
<< std::endl
<< "l = " << matrix_form(real(psi.left_vector(0)))
<< std::endl;
E = newE;
S = newS;
}
return psi;
}