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contractor.py
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contractor.py
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'''
Constractor for vmps.
'''
from numpy import *
import pdb,cPickle
from pymps import Tensor
from tba.hgen import quicksave,quickload
__all__=['Contractor']
class Contractor(object):
'''
Contraction handler.
Attributes:
:mpo/ket: <MPO>/<MPS>,the operator and ket.
:bra_labels: list, the labels for bra,
:LPART/RPART: list of <Tensor>, the result of contraction from left/right.
Readonly Attributes:
:bra: <MPS>, bra is the hermitian conjugate of ket.
'''
def __init__(self,mpo,ket,bra_bond_str='t'):
#check validity
if bra_bond_str==ket.labels[1] or bra_bond_str==mpo.labels[2] or mpo.labels[2]==ket.labels[1]: raise ValueError('Same bond string for bra, mpo and ket.')
if mpo.labels[1]!=ket.labels[0]: raise ValueError('Site string for mpo and ket do not match!')
self.bra_labels=[mpo.labels[0],bra_bond_str]
self.ket=ket
self.mpo=mpo
#initialize datas in LPART and RPART
nsite=self.ket.nsite
initial_data=Tensor(ones([1,1,1]),labels=[self.bra_labels[1]+'_0',self.mpo.get(0).labels[0],self.ket.get(0).labels[0]])
self.LPART=[initial_data]
initial_data=Tensor(ones([1,1,1]),labels=['%s_%s'%(self.bra_labels[1],nsite),self.mpo.get(nsite-1).labels[-1],self.ket.get(nsite-1).labels[-1]])
self.RPART=[initial_data]
def __str__(self):
return unicode(self).encode('utf-8')
def __unicode__(self):
mpsl='-A-'
mpsr='-A-'
mpo=u'-\u25a0-'
S=u'\u25c6'
nl=self.ket.l
nr=self.ket.nsite-self.ket.l
ketstr=mpsl*nl+S+mpsr*nr
return '%s\n%s\n%s'%(ketstr,mpo*nl+'/'+mpo*nr,ketstr)
@property
def bra(self):
return self.ket.tobra(labels=self.bra_labels)
def canomove(self,nstep,*args,**kwargs):
#self.ket.canomove(nstep,*args,**kwargs)
l0=self.ket.l
nsite=self.ket.nsite
for size in xrange(l0+1,l0+nstep+1):
self.ket>>1
self.lupdate_env(size)
for size in xrange(nsite-l0+1,nsite-l0-nstep+1):
self.ket<<1
self.rupdate_env(size)
def lupdate_env(self,i):
'''
Update LPARTs.
Parameters:
:i: int, the target length to update.
'''
if i>len(self.LPART) or i>self.ket.l: #illgal move
raise ValueError('Illegal move!')
FL=self.LPART[i-1]
cket=self.ket.get(i-1)
bs,bb=self.bra_labels
cbra=cket.conj().make_copy(['%s_%s'%(bb,i-1),'%s_%s'%(bs,i-1),'%s_%s'%(bb,i)],copydata=False)
cmpo=self.mpo.get(i-1)
FL=cbra*FL*cmpo*cket
if i==len(self.LPART): #gen new terms.
self.LPART.append(FL)
else:
self.LPART[i]=FL
self.LPART=self.LPART[:i+1]
def rupdate_env(self,i):
'''
Update RPARTs.
Parameters:
:i: int, the target length to update.
'''
nsite=self.ket.nsite
l=nsite-i
if i>len(self.RPART) or l<self.ket.l: #illgal move
raise ValueError('Illegal move!')
FR=self.RPART[i-1]
cket=self.ket.get(l)
bs,bb=self.bra_labels
cbra=cket.conj().make_copy(labels=['%s_%s'%(bb,l),'%s_%s'%(bs,l),'%s_%s'%(bb,l+1)],copydata=False)
cmpo=self.mpo.get(l)
FR=cbra*FR*cmpo*cket
if i==len(self.RPART): #gen new terms.
self.RPART.append(FR)
else:
self.RPART[i]=FR
self.RPART=self.RPART[:i+1]
def evaluate(self):
'''
Get the expectation value of mpo.
'''
nsite=self.ket.nsite
bra=self.bra
attach_S='A' if self.ket.l==nsite else 'B'
FL,FR=self.LPART[0],self.RPART[0]
for i in xrange(nsite):
cbra=bra.get(i,attach_S=attach_S)
cket=self.ket.get(i,attach_S=attach_S)
ch=self.mpo.get(i)
FL=cbra*FL*ch*cket
return (FL*FR).item()
def initialize_env(self):
'''Contract all available LPART and RPART.'''
l=self.ket.l
for size in xrange(1,l+1):
self.lupdate_env(size)
for size in xrange(1,self.ket.nsite-l+1):
self.rupdate_env(size)
def update_env_labels(self):
'''update all environment labels.'''
ket=self.ket
mpo=self.mpo
bra=self.bra
for i,E in enumerate(self.LPART):
if i!=0:
E.labels=[bra.get(i-1).labels[-1],mpo.get(i-1).labels[-1],ket.get(i-1).labels[-1]]
else:
E.labels=[bra.get(i).labels[0],mpo.get(i).labels[0],ket.get(i).labels[0]]
for i,E in enumerate(self.RPART):
ri=ket.nsite-i
if i!=0:
E.labels=[bra.get(ri).labels[0],mpo.get(ri).labels[0],ket.get(ri).labels[0]]
else:
E.labels=[bra.get(ri-1).labels[-1],mpo.get(ri-1).labels[-1],ket.get(ri-1).labels[-1]]
def keep_only(self,start,stop):
'''Remove the segment from `start` to `stop`.'''
nsite=self.ket.nsite
self.LPART=self.LPART[start:start+1]
self.RPART=self.RPART[nsite-stop:nsite-stop+1]
self.ket.remove(stop,nsite)
self.ket.remove(0,start)
self.mpo.remove(stop,nsite)
self.mpo.remove(0,start)
self.update_env_labels()
def dump_data(self,filetoken):
quicksave(filetoken+'.env.dat',(self.LPART,self.RPART))
quicksave(filetoken+'.mps.dat',self.ket)
def load_data(self,filetoken):
self.ket=quickload(filetoken+'.mps.dat')
self.LPART,self.RPART=quickload(filetoken+'.env.dat')