# Source code for qutip.simdiag

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__all__ = ['simdiag']

import numpy as np
import scipy.linalg as la
from qutip.qobj import Qobj

[docs]def simdiag(ops, evals=True):
"""Simultaneous diagonalization of commuting Hermitian matrices.

Parameters
----------
ops : list/array
list or array of qobjs representing commuting Hermitian
operators.

Returns
--------
eigs : tuple
Tuple of arrays representing eigvecs and eigvals of quantum objects
corresponding to simultaneous eigenvectors and eigenvalues for each
operator.

"""
tol = 1e-14
start_flag = 0
if not any(ops):
raise ValueError('Need at least one input operator.')
if not isinstance(ops, (list, np.ndarray)):
ops = np.array([ops])
num_ops = len(ops)
for jj in range(num_ops):
A = ops[jj]
shape = A.shape
if shape[0] != shape[1]:
raise TypeError('Matricies must be square.')
if start_flag == 0:
s = shape[0]
if s != shape[0]:
raise TypeError('All matrices. must be the same shape')
if not A.isherm:
raise TypeError('Matricies must be Hermitian')
for kk in range(jj):
B = ops[kk]
if (A * B - B * A).norm() / (A * B).norm() > tol:
raise TypeError('Matricies must commute.')

A = ops[0]
eigvals, eigvecs = la.eig(A.full())
zipped = list(zip(-eigvals, range(len(eigvals))))
zipped.sort()
ds, perm = zip(*zipped)
ds = -np.real(np.array(ds))
perm = np.array(perm)
eigvecs_array = np.array(
[np.zeros((A.shape[0], 1), dtype=complex) for k in range(A.shape[0])])

for kk in range(len(perm)):  # matrix with sorted eigvecs in columns
eigvecs_array[kk][:, 0] = eigvecs[:, perm[kk]]
k = 0
rng = np.arange(len(eigvals))
while k < len(ds):
# find degenerate eigenvalues, get indicies of degenerate eigvals
inds = np.array(abs(ds - ds[k]) < max(tol, tol * abs(ds[k])))
inds = rng[inds]
if len(inds) > 1:  # if at least 2 eigvals are degenerate
eigvecs_array[inds] = degen(
tol, eigvecs_array[inds],
np.array([ops[kk] for kk in range(1, num_ops)], dtype=object))
k = max(inds) + 1
eigvals_out = np.zeros((num_ops, len(ds)), dtype=float)
kets_out = np.array([Qobj(eigvecs_array[j] / la.norm(eigvecs_array[j]),
dims=[ops[0].dims[0], [1]],
shape=[ops[0].shape[0], 1])
for j in range(len(ds))], dtype=object)
if not evals:
return kets_out
else:
for kk in range(num_ops):
for j in range(len(ds)):
eigvals_out[kk, j] = np.real(np.dot(
eigvecs_array[j].conj().T,
ops[kk].data * eigvecs_array[j]))
return eigvals_out, kets_out

def degen(tol, in_vecs, ops):
"""
Private function that finds eigen vals and vecs for degenerate matrices..
"""
n = len(ops)
if n == 0:
return in_vecs
A = ops[0]
vecs = np.column_stack(in_vecs)
eigvals, eigvecs = la.eig(np.dot(vecs.conj().T, A.data.dot(vecs)))
zipped = list(zip(-eigvals, range(len(eigvals))))
zipped.sort()
ds, perm = zip(*zipped)
ds = -np.real(np.array(ds))
perm = np.array(perm)
vecsperm = np.zeros(eigvecs.shape, dtype=complex)
for kk in range(len(perm)):  # matrix with sorted eigvecs in columns
vecsperm[:, kk] = eigvecs[:, perm[kk]]
vecs_new = np.dot(vecs, vecsperm)
vecs_out = np.array(
[np.zeros((A.shape[0], 1), dtype=complex) for k in range(len(ds))])
for kk in range(len(perm)):  # matrix with sorted eigvecs in columns
vecs_out[kk][:, 0] = vecs_new[:, kk]
k = 0
rng = np.arange(len(ds))
while k < len(ds):
inds = np.array(abs(ds - ds[k]) < max(
tol, tol * abs(ds[k])))  # get indicies of degenerate eigvals
inds = rng[inds]
if len(inds) > 1:  # if at least 2 eigvals are degenerate
vecs_out[inds] = degen(tol, vecs_out[inds],
np.array([ops[jj] for jj in range(1, n)],
dtype=object))
k = max(inds) + 1
return vecs_out