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fix epsilon handling for signed models in sse4 #104

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egull merged 1 commit into from
Jul 21, 2026
Merged

fix epsilon handling for signed models in sse4 #104

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55 changes: 33 additions & 22 deletions applications/qmc/sse4/model.h
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Original file line number Diff line number Diff line change
Expand Up @@ -71,29 +71,39 @@ class Model {

typedef boost::multi_array<double, 2> site_tensor_type;
typedef boost::multi_array<double, 4> bond_tensor_type;

Model(alps::Parameters const& params,
model_type& model, lattice_type& lattice) :
model(model),
lattice(lattice),
params(params)
{
epsilon = params.value_or_default("EPSILON", 0.0);
if (epsilon <= 0.0 && model.is_signed())
std::cout << "Warning: Hamiltonian has a sign problem and EPSILON=0; "
"make sure that EPSILON is ergodic.\n";

_nbstates.resize(lattice.max_site_type() + 1);
for (unsigned i = 0; i < lattice.nsites(); ++i) {
unsigned stype = lattice.sitei2alps_type(i);
_nbstates[stype] = model.site_basis(stype).num_states();
}

_raising_matrix_elements.resize(lattice.max_site_type() + 1);
_lowering_matrix_elements.resize(lattice.max_site_type() + 1);

construct_vertices();
model_type& model, lattice_type& lattice) :
model(model),
lattice(lattice),
params(params)
{
epsilon = params.value_or_default("EPSILON", 0.0);

_nbstates.resize(lattice.max_site_type() + 1);
for (unsigned i = 0; i < lattice.nsites(); ++i) {
unsigned stype = lattice.sitei2alps_type(i);
_nbstates[stype] = model.site_basis(stype).num_states();
}

_raising_matrix_elements.resize(lattice.max_site_type() + 1);
_lowering_matrix_elements.resize(lattice.max_site_type() + 1);

construct_vertices();

if (epsilon <= 0.0 && model.is_signed()) {
epsilon = *std::max_element(
_max_diag_me.begin(),
_max_diag_me.end()
);

std::cout
<< "Warning: Hamiltonian has a sign problem and EPSILON<=0.\n"
<< "Automatically setting EPSILON = "
<< epsilon
<< " (largest diagonal matrix element).\n";
}
}

std::vector<unsigned> const& nbstates() const
{
Expand Down Expand Up @@ -279,7 +289,8 @@ class Model {
unsigned nneighbors0 = lattice.nneighbors(sites[0]);
unsigned nneighbors1 = lattice.nneighbors(sites[1]);

_max_diag_me[i] = std::numeric_limits<double>::min();
// _max_diag_me[i] = std::numeric_limits<double>::min();
_max_diag_me[i] = std::numeric_limits<double>::lowest();

for (unsigned l = 0; l < nstates[i]; ++l) {
vertex_type vertex;
Expand Down
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