def __init__(self, bra, ket, center=0):
assert bra.size == ket.size
#
# At the beginning, we create the right- and left- environments for
# all sites to the left and to the right of 'center', which is the
# focus point of 'LinearForm'.
#
size = bra.size
ρ = begin_environment()
R = [ρ] * size
for i in range(size-1, center, -1):
R[i-1] = ρ = update_right_environment(bra[i], ket[i], ρ)
ρ = begin_environment()
L = [ρ] * size
for i in range(0, center):
L[i+1] = ρ = update_left_environment(bra[i], ket[i], ρ)
self.bra = bra
self.ket = ket
self.size = size
self.R = R
self.L = L
self.center = center
def right_environment(self, site):
start = max(site, self.center)
ρ = expectation.begin_environment(self[start].shape[-1])
for A in self[start:site:-1]:
ρ = expectation.update_right_environment(A, A, ρ)
return ρ
def right_environment(self, site):
ρ = expectation.begin_environment()
for A in self[-1:site:-1]:
ρ = expectation.update_right_environment(A, A, ρ)
return ρ
def left_environment(self, site):
start = min(site, self.center)
ρ = expectation.begin_environment(self[start].shape[0])
for A in self[start:site]:
ρ = expectation.update_left_environment(A, A, ρ)
return ρ
def left_environment(self, site):
ρ = expectation.begin_environment()
for A in self[:site]:
ρ = expectation.update_left_environment(A, A, ρ)
return ρ