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"""Functions for resconstructing a periodic set up to isometry from its |
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PDD. This is possible 'in a general position', see our papers for more. |
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""" |
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from itertools import combinations, permutations, product |
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import numpy as np |
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import numpy.typing as npt |
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import numba |
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from scipy.spatial.distance import cdist |
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from scipy.spatial import KDTree |
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from ._nearest_neighbours import generate_concentric_cloud |
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from .utils import diameter |
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def reconstruct( |
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pdd: npt.NDArray, |
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cell: npt.NDArray |
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) -> npt.NDArray: |
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"""Reconstruct a motif from a PDD and unit cell. This function will |
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only work if ``pdd`` has enough columns, such that the last column |
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has all values larger than 2 times the diameter of the unit cell. It |
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also expects an uncollapsed PDD with no weights column. Do not use |
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``amd.PDD`` to compute the PDD for this function, instead use |
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``amd.PDD_reconstructable`` which returns a version of the PDD which |
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is passable to this function. This function is quite slow and run |
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time may vary a lot arbitrarily depending on input. |
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Parameters |
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---------- |
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pdd : :class:`numpy.ndarray` |
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The PDD of the periodic set to reconstruct. Needs `k` at least |
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large enough so all values in the last column of pdd are greater |
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than :code:`2 * diameter(cell)`, and needs to be uncollapsed |
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without weights. Use amd.PDD_reconstructable to get a PDD which |
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is acceptable for this argument. |
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cell : :class:`numpy.ndarray` |
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Unit cell of the periodic set to reconstruct. |
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Returns |
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------- |
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:class:`numpy.ndarray` |
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The reconstructed motif of the periodic set. |
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""" |
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# TODO: get a more reduced neighbour set |
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# TODO: find all shared distances in a big operation at the start |
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# TODO: move PREC variable to its proper place |
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PREC = 1e-10 |
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dims = cell.shape[0] |
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if dims not in (2, 3): |
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raise ValueError( |
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'Reconstructing from PDD only implemented for 2 and 3 dimensions' |
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) |
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diam = diameter(cell) |
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# set first point as origin wlog, return if 1 motif point |
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motif = [np.zeros((dims, ))] |
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if pdd.shape[0] == 1: |
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motif = np.array(motif) |
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return motif |
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# finding lattice distances so we can ignore them |
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cloud_generator = generate_concentric_cloud(np.array(motif), cell) |
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cloud = [] |
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next(cloud_generator) |
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layer = next(cloud_generator) |
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while np.any(np.linalg.norm(layer, axis=-1) <= diam): |
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cloud.append(layer) |
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layer = next(cloud_generator) |
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cloud = np.concatenate(cloud) |
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# is (a superset of) lattice points close enough to Voronoi domain |
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nn_set = _neighbour_set(cell, PREC) |
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lattice_dists = np.linalg.norm(cloud, axis=-1) |
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lattice_dists = lattice_dists[lattice_dists <= diam] |
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lattice_dists = _unique_within_tol(lattice_dists, PREC) |
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# remove lattice distances from first and second rows |
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row1_reduced = _remove_vals(pdd[0], lattice_dists, PREC) |
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row2_reduced = _remove_vals(pdd[1], lattice_dists, PREC) |
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# get shared dists between first and second rows |
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shared_dists = _shared_vals(row1_reduced, row2_reduced, PREC) |
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shared_dists = _unique_within_tol(shared_dists, PREC) |
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# all combinations of vecs in neighbour set forming a basis |
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bases = [] |
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for vecs in combinations(nn_set, dims): |
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vecs = np.asarray(vecs) |
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if np.abs(np.linalg.det(vecs)) > PREC: |
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bases.extend(basis for basis in permutations(vecs, dims)) |
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q = _find_second_point(shared_dists, bases, cloud, PREC) |
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if q is None: |
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raise RuntimeError('Second point of motif could not be found.') |
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motif.append(q) |
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if pdd.shape[0] == 2: |
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motif = np.array(motif) |
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return motif |
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for row in pdd[2:, :]: |
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row_reduced = _remove_vals(row, lattice_dists, PREC) |
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shared_dists1 = _shared_vals(row1_reduced, row_reduced, PREC) |
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shared_dists2 = _shared_vals(row2_reduced, row_reduced, PREC) |
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shared_dists1 = _unique_within_tol(shared_dists1, PREC) |
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shared_dists2 = _unique_within_tol(shared_dists2, PREC) |
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q_ = _find_further_point( |
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shared_dists1, shared_dists2, bases, cloud, q, PREC |
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) |
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if q_ is None: |
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raise RuntimeError('Further point of motif could not be found.') |
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motif.append(q_) |
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motif = np.array(motif) |
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motif = np.mod(motif @ np.linalg.inv(cell), 1) @ cell |
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return motif |
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def _find_second_point(shared_dists, bases, cloud, prec): |
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dims = cloud.shape[-1] |
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abs_q = shared_dists[0] |
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for distance_tup in combinations(shared_dists[1:], dims): |
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for basis in bases: |
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res = None |
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if dims == 2: |
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res = _bilaterate(*basis, *distance_tup, abs_q, prec) |
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elif dims == 3: |
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if not _four_sphere_pairwise_intersecion( |
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*basis, *distance_tup, abs_q, prec |
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): |
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continue |
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res = _trilaterate(*basis, *distance_tup, abs_q, prec) |
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if res is not None: |
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cloud_res_dists = np.linalg.norm(cloud - res, axis=-1) |
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if np.all(cloud_res_dists - abs_q + prec > 0): |
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return res |
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def _find_further_point(shared_dists1, shared_dists2, bases, cloud, q, prec): |
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# distance from origin (first motif point) to further point |
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dims = cloud.shape[-1] |
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abs_q_ = shared_dists1[0] |
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# try all ordered subsequences of distances shared between first and |
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# further row, with all combinations of the vectors in the neighbour set |
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# forming a basis |
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for distance_tup in combinations(shared_dists1[1:], dims): |
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for basis in bases: |
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res = None |
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if dims == 2: |
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res = _bilaterate(*basis, *distance_tup, abs_q_, prec) |
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elif dims == 3: |
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if not _four_sphere_pairwise_intersecion( |
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*basis, *distance_tup, abs_q_, prec |
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): |
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continue |
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res = _trilaterate(*basis, *distance_tup, abs_q_, prec) |
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if res is not None: |
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# check point is in the voronoi domain |
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cloud_res_dists = np.linalg.norm(cloud - res, axis=-1) |
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if np.all(cloud_res_dists - abs_q_ + prec > 0): |
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# check |p - point| is among the row's shared distances |
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dist_diff = np.abs(shared_dists2 - np.linalg.norm(q - res)) |
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if np.any(dist_diff < prec): |
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return res |
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def _neighbour_set(cell, prec): |
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"""(A superset of) the neighbour set of origin for a lattice.""" |
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k_ = 5 |
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coeffs = np.array(list(product((-1, 0, 1), repeat=cell.shape[0]))) |
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coeffs = coeffs[coeffs.any(axis=-1)] # remove (0,0,0) |
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# half of all combinations of basis vectors |
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vecs = [] |
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for c in coeffs: |
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vecs.append(np.sum(cell * c[None, :].T, axis=0) / 2) |
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vecs = np.array(vecs) |
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origin = np.zeros((1, cell.shape[0])) |
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cloud_generator = generate_concentric_cloud(origin, cell) |
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cloud = np.concatenate((next(cloud_generator), next(cloud_generator))) |
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tree = KDTree(cloud, compact_nodes=False, balanced_tree=False) |
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dists, inds = tree.query(vecs, k=k_, workers=-1) |
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dists_ = np.empty_like(dists) |
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while not np.allclose(dists, dists_, atol=0, rtol=1e-12): |
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dists = dists_ |
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cloud = np.vstack((cloud, |
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next(cloud_generator), |
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next(cloud_generator))) |
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tree = KDTree(cloud, compact_nodes=False, balanced_tree=False) |
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dists_, inds = tree.query(vecs, k=k_, workers=-1) |
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tmp_inds = np.unique(inds[:, 1:].flatten()) |
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tmp_inds = tmp_inds[tmp_inds != 0] |
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neighbour_set = cloud[tmp_inds] |
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# reduce neighbour set |
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# half the lattice points and find their nearest neighbours in the lattice |
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neighbour_set_half = neighbour_set / 2 |
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# for each of these vectors, check if 0 is A nearest neighbour. |
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# so, check if the dist to 0 is leq (within tol) than dist to all other |
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# lattice points. |
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nn_norms = np.linalg.norm(neighbour_set, axis=-1) |
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halves_norms = nn_norms / 2 |
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halves_to_lattice_dists = cdist(neighbour_set_half, neighbour_set) |
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# Do I need to + PREC? |
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# inds of voronoi neighbours in cloud |
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voronoi_neighbours = np.all( |
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halves_to_lattice_dists - halves_norms + prec >= 0, axis=-1 |
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) |
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neighbour_set = neighbour_set[voronoi_neighbours] |
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return neighbour_set |
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def _four_sphere_pairwise_intersecion(p1, p2, p3, r1, r2, r3, abs_val, prec): |
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"""Return True if four spheres intersect at a point.""" |
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if np.linalg.norm(p1) > abs_val + r1 - prec: |
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return False |
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if np.linalg.norm(p2) > abs_val + r2 - prec: |
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return False |
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if np.linalg.norm(p3) > abs_val + r3 - prec: |
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return False |
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if np.linalg.norm(p1 - p2) > r1 + r2 - prec: |
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return False |
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if np.linalg.norm(p1 - p3) > r1 + r3 - prec: |
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return False |
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if np.linalg.norm(p2 - p3) > r2 + r3 - prec: |
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return False |
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return True |
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@numba.njit() |
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def _bilaterate(p1, p2, r1, r2, abs_val, prec): |
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"""Return True if three circles intersect at a point.""" |
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d = np.sqrt((p2[0] - p1[0]) ** 2 + (p2[1] - p1[1]) ** 2) |
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v = (p2 - p1) / d |
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if d > r1 + r2: |
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return None |
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if d < abs(r1 - r2): |
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return None |
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if d == 0 and r1 == r2: |
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return None |
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a = (r1 ** 2 - r2 ** 2 + d ** 2) / (2 * d) |
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h = np.sqrt(r1 ** 2 - a ** 2) |
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x2 = p1[0] + a * v[0] |
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y2 = p1[1] + a * v[1] |
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x3 = x2 + h * v[1] |
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y3 = y2 - h * v[0] |
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x4 = x2 - h * v[1] |
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y4 = y2 + h * v[0] |
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q1 = np.array((x3, y3)) |
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q2 = np.array((x4, y4)) |
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if np.abs(np.sqrt(x3 ** 2 + y3 ** 2) - abs_val) < prec: |
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return q1 |
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if np.abs(np.sqrt(x4 ** 2 + y4 ** 2) - abs_val) < prec: |
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return q2 |
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return None |
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@numba.njit() |
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def _trilaterate(p1, p2, p3, r1, r2, r3, abs_val, prec): |
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"""Return the intersection of four spheres.""" |
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temp1 = p2 - p1 |
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d = np.linalg.norm(temp1) |
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e_x = temp1 / d |
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temp2 = p3 - p1 |
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i = np.dot(e_x, temp2) |
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temp3 = temp2 - i * e_x |
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e_y = temp3 / np.linalg.norm(temp3) |
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j = np.dot(e_y, temp2) |
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x = (r1 * r1 - r2 * r2 + d * d) / (2 * d) |
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y = (r1 * r1 - r3 * r3 - 2 * i * x + i * i + j * j) / (2 * j) |
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temp4 = r1 * r1 - x * x - y * y |
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if temp4 < 0: |
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return None |
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300
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e_z = np.cross(e_x, e_y) |
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z = np.sqrt(temp4) |
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p_12_a = p1 + x * e_x + y * e_y + z * e_z |
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p_12_b = p1 + x * e_x + y * e_y - z * e_z |
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if np.abs(np.linalg.norm(p_12_a) - abs_val) < prec: |
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return p_12_a |
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if np.abs(np.linalg.norm(p_12_b) - abs_val) < prec: |
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return p_12_b |
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return None |
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def _unique_within_tol(arr, prec): |
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"""Return only unique values in a vector within ``prec``.""" |
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return arr[~np.any(np.triu(np.abs(arr[:, None] - arr) < prec, 1), axis=0)] |
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def _remove_vals(vec, vals_to_remove, prec): |
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"""Remove specified values in vec, within ``prec``.""" |
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return vec[~np.any(np.abs(vec[:, None] - vals_to_remove) < prec, axis=-1)] |
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def _shared_vals(v1, v2, prec): |
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"""Return values shared between v1, v2 within ``prec``.""" |
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|
return v1[np.argwhere(np.abs(v1[:, None] - v2) < prec)[:, 0]] |
325
|
|
|
|