Verified Commit 4dd8bb7d authored by Tómas's avatar Tómas Committed by Anton Akhmerov

add sparse option and a heuristic for using it in symmetry analysis

parent 54dee7ac
Pipeline #15600 passed with stages
in 42 minutes and 41 seconds
......@@ -409,7 +409,8 @@ def _get_builder_symmetries(builder):
def find_builder_symmetries(builder, momenta=None, params=None,
spatial_symmetries=True, prettify=True):
spatial_symmetries=True, prettify=True,
"""Finds the symmetries of a Kwant system using qsymm.
......@@ -430,6 +431,12 @@ def find_builder_symmetries(builder, momenta=None, params=None,
Whether to carry out sparsification of the continuous symmetry
generators, in general an arbitrary linear combination of the
symmetry generators is returned.
sparse : bool, or None (default None)
Whether to use sparse linear algebra in the calculation.
Can give large performance gain in large systems.
If None, uses sparse or dense computation depending on
the size of the Hamiltonian.
......@@ -443,6 +450,10 @@ def find_builder_symmetries(builder, momenta=None, params=None,
ham = builder_to_model(builder, momenta=momenta,
real_space=False, params=params)
# Use dense or sparse computation depending on Hamiltonian size
if sparse is None:
sparse = list(ham.values())[0].shape[0] > 20
dim = len(np.array(builder.symmetry.periods))
if spatial_symmetries:
......@@ -455,5 +466,6 @@ def find_builder_symmetries(builder, momenta=None, params=None,
qsymm.PointGroupElement(np.eye(dim), True, True, None), # P
qsymm.PointGroupElement(np.eye(dim), False, True, None)] # C
sg, cg = qsymm.symmetries(ham, candidates, prettify=prettify,
return list(sg) + list(cg)
......@@ -404,14 +404,27 @@ def test_find_builder_discrete_symmetries():
bulk[lat(0, 0)] = h_ons
bulk[kwant.builder.HoppingKind((1, 0), lat)] = h_hop
bulk[kwant.builder.HoppingKind((0, 1), lat)] = h_hop
builder_symmetries = find_builder_symmetries(bulk, spatial_symmetries=True, prettify=True)
builder_symmetries_default = find_builder_symmetries(bulk, spatial_symmetries=True,
builder_symmetries_sparse = find_builder_symmetries(bulk, spatial_symmetries=True,
prettify=True, sparse=True)
builder_symmetries_dense = find_builder_symmetries(bulk, spatial_symmetries=True,
prettify=True, sparse=False)
assert len(builder_symmetries_default) == len(builder_symmetries_sparse)
assert len(builder_symmetries_default) == len(builder_symmetries_dense)
# Equality of symmetries ignores unitary part
fourfold_rotation = qsymm.PointGroupElement(np.array([[0, 1],[1, 0]]), False, False, None)
assert fourfold_rotation in builder_symmetries
assert fourfold_rotation in builder_symmetries_default
assert fourfold_rotation in builder_symmetries_sparse
assert fourfold_rotation in builder_symmetries_dense
class_symmetries = class_dict[sym]
for class_symmetry in class_symmetries:
assert sym_dict[class_symmetry] in builder_symmetries
assert sym_dict[class_symmetry] in builder_symmetries_default
assert sym_dict[class_symmetry] in builder_symmetries_sparse
assert sym_dict[class_symmetry] in builder_symmetries_dense
def random_onsite_hop(n, rng=0):
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