def expectation1(self, operator, site=None):
"""Return the expectated value of `operator` acting on the given `site`."""
if site is None or site == self.center:
A = self._data[self.center]
return np.vdot(A, np.einsum('ij,ajb->aib', operator, A))
else:
return expectation.expectation1(self, operator, site)
def tensor1siteok(self, aϕ, O):
for center in range(aϕ.size):
ϕ = CanonicalMPS(aϕ, center=center, normalize=True)
for n in range(ϕ.size):
#
# Take an MPS Φ, construct a new state ψ = O1*ϕ with a local
# operator on the 'n-th' site
#
ψ = mps.state.MPS(ϕ)
ψ[n] = np.einsum('ij,ajb->aib', O, ψ[n])
#
# and make sure that the AntilinearForm provides the right tensor to
# compute <ϕ|ψ> = <ϕ|O1|ϕ>
#
Odesired = expectation1(ϕ, O, n)
LF = AntilinearForm(ϕ, ψ, center)
Oestimate = np.einsum('aib,aib', ϕ[center].conj(),
LF.tensor1site())
self.assertAlmostEqual(Oestimate, Odesired)
if n >= center:
self.assertTrue(almostIdentity(LF.L[center], +1))
if n <= center:
self.assertTrue(almostIdentity(LF.R[center], +1))
def expectation1(self, operator, n):
"""Return the expectation value of `operator` acting on the `n`-th
site of the MPS. See `mps.expectation.expectation1()`."""
return expectation.expectation1(self, operator, n)