Commit c70c780c authored by Pablo Piskunow's avatar Pablo Piskunow
Browse files

fix docstrings and internal namings

parent 78bacb54
......@@ -30,11 +30,11 @@ class SpectralDensity:
In general
.. math::
ρ_A(e) = ρ(e) A(e),
ρ_A(E) = ρ(E) A(E),
where :math:`ρ(e) = \sum_{k=0}^{D-1} δ(E-E_k)` is the density of
states, and :math:`A(e)` is the expectation value of :math:`A` for
all the eigenstates with energy :math:`e`.
where :math:`ρ(E) = \\sum_{k=0}^{D-1} δ(E-E_k)` is the density of
states, and :math:`A(E)` is the expectation value of :math:`A` for
all the eigenstates with energy :math:`E`.
......@@ -45,7 +45,7 @@ class SpectralDensity:
operator : operator, dense matrix, or sparse matrix, optional
Operator for which the spectral density will be evaluated. If
it is callable, the ``densities`` at each energy will have the
dimension of the result of `operator(bra, ket)`. If it has a
dimension of the result of ``operator(bra, ket)``. If it has a
``dot`` method, such as ``numpy.ndarray`` and
``scipy.sparse.matrices``, the densities will be scalars.
If no operator is provided, the density of states is calculated
......@@ -54,7 +54,7 @@ class SpectralDensity:
Number of random vectors for the KPM method.
num_moments : positive int, default: 100
Number of moments, order of the KPM expansion. Mutually exclusive
with 'energy_resolution'.
with ``energy_resolution``.
energy_resolution : positive float, optional
The resolution in energy of the KPM approximation to the spectral
density. Mutually exclusive with 'num_moments'.
......@@ -76,10 +76,22 @@ class SpectralDensity:
not provided). If not provided, numpy's rng will be used; if it
is an Integer, it will be used to seed numpy's rng, and if it is
a random number generator, this is the one used.
kernel : callable, optional
Callable that takes moments and returns stabilized moments.
By default, the `~kwant.kpm.jackson_kernel` is used.
The Lorentz kernel is also accesible by passing
mean : bool, default: ``True``
If ``True``, return the mean spectral density for the vectors
used, otherwise return an array of densities for each vector.
accumulate_vectors : bool, default: ``True``
Whether to save or discard each vector produced by the vector
factory. If it is set to ``False``, it is not possible to
increase the number of moments, but less memory is used.
When passing an ``operator`` defined in `~kwant.operator`, the
When passing an operator defined in `~kwant.operator`, the
result of ``operator(bra, ket)`` depends on the attribute ``sum``
of such operator. If ``sum=True``, densities will be scalars, that
is, total densities of the system. If ``sum=False`` the densities
......@@ -109,7 +121,7 @@ class SpectralDensity:
>>> lat = kwant.lattice.honeycomb()
>>> syst = kwant.Builder()
>>> syst[lat.shape(circle, (0, 0))] = 0
>>> syst[lat.neighbors()] = 1
>>> syst[lat.neighbors()] = -1
and after finalizing the system, create an instance of
......@@ -152,7 +164,7 @@ class SpectralDensity:
hamiltonian = hamiltonian.hamiltonian_submatrix(params=params,
hamiltonian = scipy.sparse.csr_matrix(hamiltonian)
hamiltonian = csr_matrix(hamiltonian)
except Exception:
raise ValueError("'hamiltonian' is neither a matrix "
"nor a Kwant system.")
......@@ -165,11 +177,11 @@ class SpectralDensity:
elif callable(operator):
self.operator = operator
elif hasattr(operator, 'dot'):
operator = scipy.sparse.csr_matrix(operator)
operator = csr_matrix(operator)
self.operator = lambda bra, ket: np.vdot(bra,
raise ValueError('Parameter `operator` has no `.dot` '
'attribute and is not callable.')
raise ValueError("Parameter 'operator' has no '.dot' "
"attribute and is not callable.")
self._vector_factory = vector_factory or \
(lambda n: np.exp(2j * np.pi * rng.random_sample(n)))
......@@ -188,43 +200,59 @@ class SpectralDensity:
elif num_moments is None:
num_moments = 100
must_be_positive_int = ['num_vectors', 'num_moments']
for var in must_be_positive_int:
val = locals()[var]
if val <= 0 or val != int(val):
raise ValueError('{} must be a positive integer'.format(var))
if num_moments <= 0 or num_moments != int(num_moments):
raise ValueError("'num_moments' must be a positive integer")
if eps <= 0:
raise ValueError('eps must be positive')
raise ValueError("'eps' must be positive")
for r in range(num_vectors):
self._last_two_alphas = [0.] * num_vectors
self._moments_list = [0.] * num_vectors
if vector_factory is None:
self._vector_factory = _VectorFactory(
RandomVectors(hamiltonian, rng=rng),
self._vector_factory = _VectorFactory(
num_vectors = self._vector_factory.num_vectors
self._last_two_alphas = []
self._moments_list = []
self.num_moments = num_moments
self.num_vectors = 0 # new random vectors will be used
self._update_moments_list(self.num_moments, num_vectors)
self.num_vectors = num_vectors
# set kernel before calling moments
self.kernel = kernel if kernel is not None else jackson_kernel
moments = self._moments()
xk_rescaled, rho, self._gammas = _calc_fft_moments(
moments, 2 * self.num_moments)
self.energies = xk_rescaled * self._a + self._b
self.densities = rho
self.densities, self._gammas = _calc_fft_moments(moments)
def energies(self):
return (self._a * _chebyshev_nodes(SAMPLING * self.num_moments)
+ self._b)
def num_vectors(self):
return len(self._moments_list)
def __call__(self, energy=None):
"""Return the spectral density evaluated at ``energy``.
energy : float or sequence of float, optional
energy : float or sequence of floats, optional
float, if ``energy`` is float, array of float if ``energy``
is a sequence, a tuple (energies, densities) if
``energy`` was not provided.
``(energies, densities)`` if the ``energy`` parameter is not
provided, else ``densities``.
energies : array of floats
Drawn from the nodes of the highest Chebyshev polynomial.
densities : float or array of floats
single ``float`` if the ``energy`` parameter is a single
``float``, else an array of ``float``.
......@@ -284,11 +312,11 @@ class SpectralDensity:
num_moments: positive int
The number of Chebyshev moments to add. Mutually
exclusive with 'energy_resolution'.
exclusive with ``energy_resolution``.
energy_resolution: positive float, optional
Features wider than this resolution are visible
in the spectral density. Mutually exclusive with
if not ((num_moments is None) ^ (energy_resolution is None)):
raise TypeError("either 'num_moments' or 'energy_resolution' "
......@@ -309,7 +337,7 @@ class SpectralDensity:
num_moments = math.ceil((1.6 * self._a) / energy_resolution)
if (num_moments is None or num_moments <= 0
or num_moments != int(num_moments)):
or num_moments != int(num_moments)):
raise ValueError("'num_moments' must be a positive integer")
self._update_moments_list(self.num_moments + num_moments,
......@@ -328,8 +356,8 @@ class SpectralDensity:
num_vectors: positive int
The number of random vectors to add.
num_vectors: positive int, optional
The number of vectors to add.
if num_vectors <= 0 or num_vectors != int(num_vectors):
raise ValueError("'num_vectors' must be a positive integer")
......@@ -350,14 +378,15 @@ class SpectralDensity:
self.densities = rho
def _moments(self):
# sum moments of all random vectors
moments = np.sum(np.asarray(self._moments_list).real, axis=0)
# divide by the number of random vectors
moments /= self.num_vectors
moments = np.real_if_close(self._moments_list)
# put moments in the first axis, to return an array of densities
moments = np.swapaxes(moments, 0, 1)
if self.mean:
moments = np.mean(moments, axis=1)
# divide by scale factor to reflect the integral rescaling
return moments / self._a
def _update_moments_list(self, n_moments, n_rand):
def _update_moments_list(self, n_moments, num_vectors):
"""Calculate the Chebyshev moments of an operator's spectral
......@@ -369,23 +398,25 @@ class SpectralDensity:
n_moments : integer
Number of Chebyshev moments.
n_rand : integer
Number of random vectors used for sampling.
num_vectors : integer
Number of vectors used for sampling.
if self.num_vectors == n_rand:
if self.num_vectors == num_vectors:
r_start = 0
new_rand_vect = 0
elif self.num_vectors < n_rand:
new_vectors = 0
elif self.num_vectors < num_vectors:
r_start = self.num_vectors
new_rand_vect = n_rand - self.num_vectors
new_vectors = num_vectors - self.num_vectors
raise ValueError('Cannot decrease number of random vectors')
raise ValueError('Cannot decrease number of vectors')
self._moments_list.extend([0.] * new_vectors)
self._last_two_alphas.extend([0.] * new_vectors)
if n_moments == self.num_moments:
m_start = 2
new_moments = 0
if new_rand_vect == 0:
if new_vectors == 0:
# nothing new to calculate
......@@ -394,15 +425,15 @@ class SpectralDensity:
if new_moments < 0:
raise ValueError('Cannot decrease number of moments')
if new_rand_vect != 0:
if new_vectors != 0:
raise ValueError("Only 'num_moments' *or* 'num_vectors' "
"may be updated at a time.")
for r in range(r_start, n_rand):
alpha_zero = self._rand_vect_list[r]
for r in range(r_start, num_vectors):
alpha_zero = self._vector_factory[r]
one_moment = [0.] * n_moments
if new_rand_vect > 0:
if new_vectors > 0:
alpha = alpha_zero
alpha_next = self.hamiltonian.matvec(alpha)
if self.operator is None:
......@@ -463,7 +494,7 @@ def _rescale(hamiltonian, eps, v0, bounds):
hamiltonian : 2D array
Hamiltonian of the system.
eps : scalar
Ensures that the bounds 'a' and 'b' are strict.
Ensures that the bounds are strict.
v0 : random vector, or None
Used as the initial residual vector for the algorithm that
finds the lowest and highest eigenvalues.
......@@ -479,10 +510,10 @@ def _rescale(hamiltonian, eps, v0, bounds):
if bounds:
lmin, lmax = bounds
lmax = float(sla.eigsh(hamiltonian, k=1, which='LA',
return_eigenvectors=False, tol=tol, v0=v0))
lmin = float(sla.eigsh(hamiltonian, k=1, which='SA',
return_eigenvectors=False, tol=tol, v0=v0))
lmax = float(eigsh(hamiltonian, k=1, which='LA',
return_eigenvectors=False, tol=tol, v0=v0))
lmin = float(eigsh(hamiltonian, k=1, which='SA',
return_eigenvectors=False, tol=tol, v0=v0))
a = np.abs(lmax-lmin) / (2. - eps)
b = (lmax+lmin) / 2.
......@@ -495,7 +526,7 @@ def _rescale(hamiltonian, eps, v0, bounds):
def rescaled(v):
return ( - b * v) / a
rescaled_ham = sla.LinearOperator(shape=hamiltonian.shape, matvec=rescaled)
rescaled_ham = LinearOperator(shape=hamiltonian.shape, matvec=rescaled)
return rescaled_ham, (a, b)
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment