Example #1
0
def select_merge_components(
    curModel, Data, SS, MTracker=None, MSelector=None, mergename="marglik", randstate=np.random, kA=None, **kwargs
):
    """ Select which two existing components to merge when constructing
      a candidate "merged" model from curModel, which has K components.
      We select components kA, kB by their integer ID, in {1, 2, ... K}

      Args
      --------
      curModel : bnpy model whose components we should merge
      Data : data object 
      SS : suff stats object for Data under curModel
      LP : local params dictionary (not required except for 'overlap')
      mergename : string specifying routine for how to select kA, kB
                  options include
                  'random' : select comps at random, without using data.
                  'marglik' : select comps by marginal likelihood ratio.
      Returns
      --------
      kA : integer id of the first component to merge
      kB : integer id of the 2nd component to merge

      This method guarantees that kA < kB.
  """
    if MTracker is None:
        MTracker = MergeTracker(SS.K)
    if MSelector is None:
        MSelector = MergePairSelector()
    kA, kB = MSelector.select_merge_components(curModel, SS, MTracker, mergename=mergename, kA=kA, randstate=randstate)
    return kA, kB
Example #2
0
def select_merge_components(curModel,
                            Data,
                            SS,
                            MTracker=None,
                            MSelector=None,
                            mergename='marglik',
                            randstate=np.random,
                            kA=None,
                            **kwargs):
    ''' Select which two existing components to merge when constructing
      a candidate "merged" model from curModel, which has K components.
      We select components kA, kB by their integer ID, in {1, 2, ... K}

      Args
      --------
      curModel : bnpy model whose components we should merge
      Data : data object 
      SS : suff stats object for Data under curModel
      LP : local params dictionary (not required except for 'overlap')
      mergename : string specifying routine for how to select kA, kB
                  options include
                  'random' : select comps at random, without using data.
                  'marglik' : select comps by marginal likelihood ratio.
      Returns
      --------
      kA : integer id of the first component to merge
      kB : integer id of the 2nd component to merge

      This method guarantees that kA < kB.
  '''
    if MTracker is None:
        MTracker = MergeTracker(SS.K)
    if MSelector is None:
        MSelector = MergePairSelector()
    kA, kB = MSelector.select_merge_components(curModel,
                                               SS,
                                               MTracker,
                                               mergename=mergename,
                                               kA=kA,
                                               randstate=randstate)
    return kA, kB
Example #3
0
def preselect_all_merge_candidates(
    curModel, SS, randstate=np.random, preselectroutine="random", mergePerLap=10, compIDs=list(), **kwargs
):
    """ 
      Create and return a list of tuples,
        where each tuple represents a set of component IDs to try to merge

      Args
      --------
      curModel : bnpy HModel 
      SS : bnpy SuffStatBag. If None, defaults to random selection.
      randstate : numpy random number generator
      preselectroutine : name of procedure to select candidate pairs
                          {'random', 'marglik', 'freshallpairs'}
      mergePerLap : int number of candidates to identify 
                      (may be less if K small)            

      Returns
      --------
      mPairList : list of component ID candidates for positions kA, kB
                    each entry is a tuple of two integers
  """
    nMergeTrials = mergePerLap
    K = curModel.allocModel.K
    if SS is None:  # Handle first lap
        preselectroutine = "random"
    aList = list()
    bList = list()

    partnerIDs = set(range(K))
    partnerIDs.difference_update(compIDs)
    if preselectroutine == "allpairsfromlist":
        compIDs = sorted(compIDs)
        L = len(compIDs)
        for aa in xrange(L - 1):
            for bb in xrange(aa + 1, L):
                aList.append(compIDs[aa])
                bList.append(compIDs[bb])
        aList = aList[:nMergeTrials]
        bList = bList[:nMergeTrials]
    elif preselectroutine == "allpairsfromlistbipartite":
        compIDs = sorted(compIDs)
        L = len(compIDs)
        for kA in compIDs:
            for kB in list(partnerIDs):
                aList.append(np.minimum(kA, kB))
                bList.append(np.maximum(kA, kB))
        aList = aList[:nMergeTrials]
        bList = bList[:nMergeTrials]
    elif preselectroutine == "bestnmatchfromlist":
        # Loop thru and find 3 best pairs for each comp in list
        compIDs = sorted(compIDs)
        L = len(compIDs)
        MTracker = MergeTracker(K)
        MSelector = MergePairSelector()
        cID = 0
        trial = 0
        hasPairs = MTracker.hasAvailablePairs
        while hasPairs() and cID < L and len(aList) < nMergeTrials:
            nPartners = 0
            hasPartners = MTracker.hasAvailablePartnersForComp
            while hasPartners(compIDs[cID]) and nPartners < 3:
                kA, kB = MSelector.select_merge_components(
                    curModel, SS, MTracker, mergename="marglik", kA=compIDs[cID], randstate=randstate
                )
                MTracker.recordResult(kA=kA, kB=kB)
                aList.append(kA)
                bList.append(kB)
                nPartners += 1
                trial += 1
            cID += 1
        # reindex aList, bList so we're likely to try all compIDs once
        aList = aList[::3] + aList[1::3] + aList[2::3]
        bList = bList[::3] + bList[1::3] + bList[2::3]
        aList = aList[:nMergeTrials]
        bList = bList[:nMergeTrials]
        # at this point, we've added each fresh comp once
        # continue to add random pairs to list until we've maxed out nMergeTrials
        while MTracker.hasAvailablePairs() and trial < nMergeTrials:
            kA, kB = MSelector.select_merge_components(curModel, SS, MTracker, mergename="marglik", randstate=randstate)
            MTracker.recordResult(kA=kA, kB=kB)
            aList.append(kA)
            bList.append(kB)
            trial += 1
    elif preselectroutine == "freshbestmatch":
        compIDs = sorted(compIDs)
        L = len(compIDs)
        MTracker = MergeTracker(K)
        MSelector = MergePairSelector()
        trial = 0
        while MTracker.hasAvailablePairs() and trial < np.minimum(L, nMergeTrials):
            kA = compIDs[trial]
            kA, kB = MSelector.select_merge_components(
                curModel, SS, MTracker, mergename="marglik", kA=kA, randstate=randstate
            )
            MTracker.recordResult(kA=kA, kB=kB)
            aList.append(kA)
            bList.append(kB)
            trial += 1
        # at this point, we've added each fresh comp once
        # continue to add to list until we've maxed out nMergeTrials
        while MTracker.hasAvailablePairs() and trial < nMergeTrials:
            kA, kB = MSelector.select_merge_components(curModel, SS, MTracker, mergename="marglik", randstate=randstate)
            MTracker.recordResult(kA=kA, kB=kB)
            aList.append(kA)
            bList.append(kB)
            trial += 1

    elif preselectroutine == "random":
        MTracker = MergeTracker(K)
        MSelector = MergePairSelector()
        trial = 0
        while MTracker.hasAvailablePairs() and trial < nMergeTrials:
            trial += 1
            kA, kB = MSelector.select_merge_components(curModel, SS, MTracker, mergename="random", randstate=randstate)
            MTracker.recordResult(kA=kA, kB=kB)
            aList.append(kA)
            bList.append(kB)
    elif preselectroutine == "marglik":
        MSelector = MergePairSelector()
        M = np.zeros((K, K))
        for kA in xrange(K):
            for kB in xrange(kA + 1, K):
                M[kA, kB] = MSelector._calcMScoreForCandidatePair(curModel, SS, kA, kB)
        # find the n largest non-zero entries
        flatM = M.flatten()
        bestIDs = np.argsort(flatM)[::-1]
        bestIDs = bestIDs[flatM[bestIDs] != 0]
        bestrs, bestcs = np.unravel_index(bestIDs, M.shape)
        assert np.all(bestrs < bestcs)
        aList = bestrs[:nMergeTrials].tolist()
        bList = bestcs[:nMergeTrials].tolist()
    elif preselectroutine == "marglikfromlistbipartite":
        """ consider best candidates for each comp in list,
            only partnering with nodes outside the list
    """
        MTracker = MergeTracker(K)
        MSelector = MergePairSelector()
        M = np.zeros((K, K))
        for kA in sorted(compIDs):
            for kB in list(partnerIDs):
                M[kA, kB] = MSelector._calcMScoreForCandidatePair(curModel, SS, kA, kB)
            # find the L largest non-zero entries
            bestIDs = np.argsort(M[kA, :])[::-1]
            bestIDs = bestIDs[M[kA, bestIDs] != 0]
            bestIDs = bestIDs[:3]
            for kB in bestIDs:
                MTracker.recordResult(kA=np.minimum(kA, kB), kB=np.maximum(kA, kB))
                aList.append(np.minimum(kA, kB))
                bList.append(np.maximum(kA, kB))

        # reindex aList, bList so we're likely to try all compIDs once
        aList = aList[::3] + aList[1::3] + aList[2::3]
        bList = bList[::3] + bList[1::3] + bList[2::3]
        aList = aList[:nMergeTrials]
        bList = bList[:nMergeTrials]
    assert len(aList) == len(bList)
    assert len(aList) <= nMergeTrials
    return zip(aList, bList)
Example #4
0
def run_merge_move(
    curModel,
    Data,
    SS=None,
    curEv=None,
    doVizMerge=False,
    kA=None,
    kB=None,
    MTracker=None,
    MSelector=None,
    mergename="marglik",
    randstate=np.random.RandomState(),
    doUpdateAllComps=0,
    savedir=None,
    doVerbose=False,
    doWriteLog=False,
    **kwargs
):
    """ Creates candidate model with two components merged,
      and returns either candidate or current model,
      whichever has higher log probability (ELBO).

      Args
      --------
       curModel : bnpy model whose components will be merged
       Data : bnpy Data object 
       SS : bnpy SuffStatDict object for Data under curModel
            must contain precomputed merge entropy in order to try a merge.
       curEv : current evidence bound, provided to save re-computation.
                curEv = curModel.calc_evidence(SS=SS)
       kA, kB : (optional) integer ids for which specific components to merge
       excludeList : (optional) list of integer ids excluded when selecting
                      which components to merge. useful when doing multiple 
                      rounds of merges, since precomputed merge terms are 
                      valid for one merge only.
      Returns
      --------
      hmodel, SS, evBound, MoveInfo

      hmodel := candidate or current model (bnpy HModel object)
      SS := suff stats for Data under hmodel
      evBound := log evidence (ELBO) of Data under hmodel
      MoveInfo := dict of info about this merge move, with fields
            didAccept := boolean flag, true if candidate accepted
            msg := human-readable string about this move
            kA, kB := indices of the components to be merged.
  """
    if SS is None:
        LP = curModel.calc_local_params(Data)
        SS = curModel.get_global_suff_stats(Data, LP, doPrecompEntropy=True, doPrecompMerge=True)
    if curEv is None:
        curEv = curModel.calc_evidence(SS=SS)
    if MTracker is None:
        MTracker = MergeTracker(SS.K)
    if MSelector is None:
        MSelector = MergePairSelector()

    # Need at least two components to merge!
    if curModel.allocModel.K == 1:
        MoveInfo = dict(didAccept=0, msg="need >= 2 comps to merge")
        return curModel, SS, curEv, MoveInfo

    if not SS.hasMergeTerms() and curModel.allocModel.requireMergeTerms():
        MoveInfo = dict(didAccept=0, msg="suff stats did not have merge terms")
        return curModel, SS, curEv, MoveInfo

    if kA is not None and kA not in MTracker.getAvailableComps():
        MoveInfo = dict(didAccept=0, msg="target comp kA must be excluded.")
        return curModel, SS, curEv, MoveInfo

    # Select which 2 components kA, kB in {1, 2, ... K} to merge
    if kA is None or kB is None:
        kA, kB = select_merge_components(
            curModel, Data, SS, kA=kA, MTracker=MTracker, MSelector=MSelector, mergename=mergename, randstate=randstate
        )

    # Create candidate merged model
    propModel, propSS = propose_merge_candidate(curModel, SS, kA, kB, doUpdateAllComps=doUpdateAllComps)

    # Decide whether to accept the merge
    propEv = propModel.calc_evidence(SS=propSS)

    if np.isnan(propEv) or np.isinf(propEv):
        raise ValueError("propEv should never be nan/inf")

    if doVizMerge:
        viz_merge_proposal(curModel, propModel, kA, kB, curEv, propEv)

    evDiff = propEv - curEv

    if hasattr(SS, "nDoc") and np.abs(propEv - curEv) > 0.05 * np.abs(curEv):
        print "CRAP! ---------------------------------------!!!!$$$$$$$$"
        print "    propEv % .5e" % (propEv)
        print "    curEv  % .5e" % (curEv)
        MoveInfo = dict(didAccept=0, kA=kA, kB=kB, msg="CRAP. bad proposed evidence.")
        return curModel, SS, curEv, MoveInfo

    if hasattr(SS, "nDoc") and (propEv > 0 and curEv < 0):
        print "CRAP! ---------------------------------------!!!!@@@@@@@@"
        print "    propEv % .5e" % (propEv)
        print "    curEv  % .5e" % (curEv)
        MoveInfo = dict(didAccept=0, kA=kA, kB=kB, msg="CRAP. bad proposed evidence.")
        return curModel, SS, curEv, MoveInfo

    if propEv >= curEv:
        MSelector.reindexAfterMerge(kA, kB)
        msg = "merge %3d & %3d | ev +%.3e ****" % (kA, kB, propEv - curEv)
        MoveInfo = dict(didAccept=1, kA=kA, kB=kB, msg=msg, evDiff=evDiff)
        if doWriteLog:
            log_merge_move(MoveInfo, MSelector, curModel, SS, savedir)
        return propModel, propSS, propEv, MoveInfo
    else:
        msg = "merge %3d & %3d | ev -%.3e" % (kA, kB, curEv - propEv)
        MoveInfo = dict(didAccept=0, kA=kA, kB=kB, msg=msg, evDiff=evDiff)
        if doWriteLog:
            log_merge_move(MoveInfo, MSelector, curModel, SS, savedir)
        return curModel, SS, curEv, MoveInfo
Example #5
0
def preselect_all_merge_candidates(curModel,
                                   SS,
                                   randstate=np.random,
                                   preselectroutine='random',
                                   mergePerLap=10,
                                   compIDs=list(),
                                   **kwargs):
    ''' 
      Create and return a list of tuples,
        where each tuple represents a set of component IDs to try to merge

      Args
      --------
      curModel : bnpy HModel 
      SS : bnpy SuffStatBag. If None, defaults to random selection.
      randstate : numpy random number generator
      preselectroutine : name of procedure to select candidate pairs
                          {'random', 'marglik', 'freshallpairs'}
      mergePerLap : int number of candidates to identify 
                      (may be less if K small)            

      Returns
      --------
      mPairList : list of component ID candidates for positions kA, kB
                    each entry is a tuple of two integers
  '''
    nMergeTrials = mergePerLap
    K = curModel.allocModel.K
    if SS is None:  # Handle first lap
        preselectroutine = 'random'
    aList = list()
    bList = list()

    partnerIDs = set(range(K))
    partnerIDs.difference_update(compIDs)
    if preselectroutine == 'allpairsfromlist':
        compIDs = sorted(compIDs)
        L = len(compIDs)
        for aa in xrange(L - 1):
            for bb in xrange(aa + 1, L):
                aList.append(compIDs[aa])
                bList.append(compIDs[bb])
        aList = aList[:nMergeTrials]
        bList = bList[:nMergeTrials]
    elif preselectroutine == 'allpairsfromlistbipartite':
        compIDs = sorted(compIDs)
        L = len(compIDs)
        for kA in compIDs:
            for kB in list(partnerIDs):
                aList.append(np.minimum(kA, kB))
                bList.append(np.maximum(kA, kB))
        aList = aList[:nMergeTrials]
        bList = bList[:nMergeTrials]
    elif preselectroutine == 'bestnmatchfromlist':
        # Loop thru and find 3 best pairs for each comp in list
        compIDs = sorted(compIDs)
        L = len(compIDs)
        MTracker = MergeTracker(K)
        MSelector = MergePairSelector()
        cID = 0
        trial = 0
        hasPairs = MTracker.hasAvailablePairs
        while hasPairs() and cID < L and len(aList) < nMergeTrials:
            nPartners = 0
            hasPartners = MTracker.hasAvailablePartnersForComp
            while hasPartners(compIDs[cID]) and nPartners < 3:
                kA, kB = MSelector.select_merge_components(curModel,
                                                           SS,
                                                           MTracker,
                                                           mergename='marglik',
                                                           kA=compIDs[cID],
                                                           randstate=randstate)
                MTracker.recordResult(kA=kA, kB=kB)
                aList.append(kA)
                bList.append(kB)
                nPartners += 1
                trial += 1
            cID += 1
        # reindex aList, bList so we're likely to try all compIDs once
        aList = aList[::3] + aList[1::3] + aList[2::3]
        bList = bList[::3] + bList[1::3] + bList[2::3]
        aList = aList[:nMergeTrials]
        bList = bList[:nMergeTrials]
        # at this point, we've added each fresh comp once
        # continue to add random pairs to list until we've maxed out nMergeTrials
        while MTracker.hasAvailablePairs() and trial < nMergeTrials:
            kA, kB = MSelector.select_merge_components(curModel,
                                                       SS,
                                                       MTracker,
                                                       mergename='marglik',
                                                       randstate=randstate)
            MTracker.recordResult(kA=kA, kB=kB)
            aList.append(kA)
            bList.append(kB)
            trial += 1
    elif preselectroutine == 'freshbestmatch':
        compIDs = sorted(compIDs)
        L = len(compIDs)
        MTracker = MergeTracker(K)
        MSelector = MergePairSelector()
        trial = 0
        while MTracker.hasAvailablePairs() and trial < np.minimum(
                L, nMergeTrials):
            kA = compIDs[trial]
            kA, kB = MSelector.select_merge_components(curModel,
                                                       SS,
                                                       MTracker,
                                                       mergename='marglik',
                                                       kA=kA,
                                                       randstate=randstate)
            MTracker.recordResult(kA=kA, kB=kB)
            aList.append(kA)
            bList.append(kB)
            trial += 1
        # at this point, we've added each fresh comp once
        # continue to add to list until we've maxed out nMergeTrials
        while MTracker.hasAvailablePairs() and trial < nMergeTrials:
            kA, kB = MSelector.select_merge_components(curModel,
                                                       SS,
                                                       MTracker,
                                                       mergename='marglik',
                                                       randstate=randstate)
            MTracker.recordResult(kA=kA, kB=kB)
            aList.append(kA)
            bList.append(kB)
            trial += 1

    elif preselectroutine == 'random':
        MTracker = MergeTracker(K)
        MSelector = MergePairSelector()
        trial = 0
        while MTracker.hasAvailablePairs() and trial < nMergeTrials:
            trial += 1
            kA, kB = MSelector.select_merge_components(curModel,
                                                       SS,
                                                       MTracker,
                                                       mergename='random',
                                                       randstate=randstate)
            MTracker.recordResult(kA=kA, kB=kB)
            aList.append(kA)
            bList.append(kB)
    elif preselectroutine == 'marglik':
        MSelector = MergePairSelector()
        M = np.zeros((K, K))
        for kA in xrange(K):
            for kB in xrange(kA + 1, K):
                M[kA, kB] = MSelector._calcMScoreForCandidatePair(
                    curModel, SS, kA, kB)
        # find the n largest non-zero entries
        flatM = M.flatten()
        bestIDs = np.argsort(flatM)[::-1]
        bestIDs = bestIDs[flatM[bestIDs] != 0]
        bestrs, bestcs = np.unravel_index(bestIDs, M.shape)
        assert np.all(bestrs < bestcs)
        aList = bestrs[:nMergeTrials].tolist()
        bList = bestcs[:nMergeTrials].tolist()
    elif preselectroutine == 'marglikfromlistbipartite':
        ''' consider best candidates for each comp in list,
            only partnering with nodes outside the list
    '''
        MTracker = MergeTracker(K)
        MSelector = MergePairSelector()
        M = np.zeros((K, K))
        for kA in sorted(compIDs):
            for kB in list(partnerIDs):
                M[kA, kB] = MSelector._calcMScoreForCandidatePair(
                    curModel, SS, kA, kB)
            # find the L largest non-zero entries
            bestIDs = np.argsort(M[kA, :])[::-1]
            bestIDs = bestIDs[M[kA, bestIDs] != 0]
            bestIDs = bestIDs[:3]
            for kB in bestIDs:
                MTracker.recordResult(kA=np.minimum(kA, kB),
                                      kB=np.maximum(kA, kB))
                aList.append(np.minimum(kA, kB))
                bList.append(np.maximum(kA, kB))

        # reindex aList, bList so we're likely to try all compIDs once
        aList = aList[::3] + aList[1::3] + aList[2::3]
        bList = bList[::3] + bList[1::3] + bList[2::3]
        aList = aList[:nMergeTrials]
        bList = bList[:nMergeTrials]
    assert len(aList) == len(bList)
    assert len(aList) <= nMergeTrials
    return zip(aList, bList)
Example #6
0
def run_many_merge_moves(hmodel,
                         Data,
                         SS,
                         evBound=None,
                         nMergeTrials=1,
                         compList=list(),
                         randstate=np.random,
                         mPairIDs=None,
                         **mergeKwArgs):
    ''' Run (potentially many) merge move on hmodel

      Args
      -------
      hmodel
      Data
      SS
      nMergeTrials : number of merges to try
      compList : list of components to include in attempted merges
      randstate : numpy random number generator

      Returns
      -------
      hmodel
      SS
      evBound
      MTracker
  '''
    nMergeTrials = np.maximum(nMergeTrials, len(compList))

    MTracker = MergeTracker(SS.K)
    MSelector = MergePairSelector()

    # Exclude all pairs for which we did not compute the combined entropy Hz
    #  Hz is always stored in KxK matrix. Pairs that were skipped have zeros.
    aList = list()
    bList = list()
    if SS.hasMergeTerm('ElogqZ'):
        Hz = SS.getMergeTerm('ElogqZ')
        for kA in xrange(SS.K):
            for kB in xrange(kA + 1, SS.K):
                if Hz[kA, kB] == 0:
                    aList.append(kA)
                    bList.append(kB)
    if len(aList) > 0:
        MTracker.addPairsToExclude(aList, bList)

    if evBound is None:
        newEv = hmodel.calc_evidence(SS=SS)
    else:
        newEv = evBound

    trialID = 0
    shift = np.zeros(SS.K, dtype=np.int32)
    while trialID < nMergeTrials and MTracker.hasAvailablePairs():
        oldEv = newEv

        if mPairIDs is not None:
            if len(mPairIDs) == 0:
                break
            kA, kB = mPairIDs.pop(0)
            try:
                MTracker.verifyPair(kA, kB)
            except AssertionError:
                print '  AssertionError skipped with mPairIDs!', kA, kB
                continue
        elif len(compList) > 0:
            kA = compList.pop()
            if kA not in MTracker.getAvailableComps():
                continue
            kB = None
        else:
            kA = None
            kB = None

        hmodel, SS, newEv, MoveInfo = run_merge_move(hmodel,
                                                     Data,
                                                     SS,
                                                     oldEv,
                                                     kA=kA,
                                                     kB=kB,
                                                     randstate=randstate,
                                                     MSelector=MSelector,
                                                     MTracker=MTracker,
                                                     **mergeKwArgs)
        if MoveInfo['didAccept']:
            assert newEv >= oldEv
            if mPairIDs is not None:
                mPairIDs = _reindexCandidatePairsAfterAcceptedMerge(
                    mPairIDs, kA, kB)
        trialID += 1
        MTracker.recordResult(**MoveInfo)

    return hmodel, SS, newEv, MTracker
Example #7
0
def run_merge_move(curModel,
                   Data,
                   SS=None,
                   curEv=None,
                   doVizMerge=False,
                   kA=None,
                   kB=None,
                   MTracker=None,
                   MSelector=None,
                   mergename='marglik',
                   randstate=np.random.RandomState(),
                   doUpdateAllComps=0,
                   savedir=None,
                   doVerbose=False,
                   doWriteLog=False,
                   **kwargs):
    ''' Creates candidate model with two components merged,
      and returns either candidate or current model,
      whichever has higher log probability (ELBO).

      Args
      --------
       curModel : bnpy model whose components will be merged
       Data : bnpy Data object 
       SS : bnpy SuffStatDict object for Data under curModel
            must contain precomputed merge entropy in order to try a merge.
       curEv : current evidence bound, provided to save re-computation.
                curEv = curModel.calc_evidence(SS=SS)
       kA, kB : (optional) integer ids for which specific components to merge
       excludeList : (optional) list of integer ids excluded when selecting
                      which components to merge. useful when doing multiple 
                      rounds of merges, since precomputed merge terms are 
                      valid for one merge only.
      Returns
      --------
      hmodel, SS, evBound, MoveInfo

      hmodel := candidate or current model (bnpy HModel object)
      SS := suff stats for Data under hmodel
      evBound := log evidence (ELBO) of Data under hmodel
      MoveInfo := dict of info about this merge move, with fields
            didAccept := boolean flag, true if candidate accepted
            msg := human-readable string about this move
            kA, kB := indices of the components to be merged.
  '''
    if SS is None:
        LP = curModel.calc_local_params(Data)
        SS = curModel.get_global_suff_stats(Data,
                                            LP,
                                            doPrecompEntropy=True,
                                            doPrecompMerge=True)
    if curEv is None:
        curEv = curModel.calc_evidence(SS=SS)
    if MTracker is None:
        MTracker = MergeTracker(SS.K)
    if MSelector is None:
        MSelector = MergePairSelector()

    # Need at least two components to merge!
    if curModel.allocModel.K == 1:
        MoveInfo = dict(didAccept=0, msg="need >= 2 comps to merge")
        return curModel, SS, curEv, MoveInfo

    if not SS.hasMergeTerms() and curModel.allocModel.requireMergeTerms():
        MoveInfo = dict(didAccept=0, msg="suff stats did not have merge terms")
        return curModel, SS, curEv, MoveInfo

    if kA is not None and kA not in MTracker.getAvailableComps():
        MoveInfo = dict(didAccept=0, msg="target comp kA must be excluded.")
        return curModel, SS, curEv, MoveInfo

    # Select which 2 components kA, kB in {1, 2, ... K} to merge
    if kA is None or kB is None:
        kA, kB = select_merge_components(curModel,
                                         Data,
                                         SS,
                                         kA=kA,
                                         MTracker=MTracker,
                                         MSelector=MSelector,
                                         mergename=mergename,
                                         randstate=randstate)

    # Create candidate merged model
    propModel, propSS = propose_merge_candidate(
        curModel, SS, kA, kB, doUpdateAllComps=doUpdateAllComps)

    # Decide whether to accept the merge
    propEv = propModel.calc_evidence(SS=propSS)

    if np.isnan(propEv) or np.isinf(propEv):
        raise ValueError('propEv should never be nan/inf')

    if doVizMerge:
        viz_merge_proposal(curModel, propModel, kA, kB, curEv, propEv)

    evDiff = propEv - curEv

    if hasattr(SS, 'nDoc') and np.abs(propEv - curEv) > 0.05 * np.abs(curEv):
        print 'CRAP! ---------------------------------------!!!!$$$$$$$$'
        print '    propEv % .5e' % (propEv)
        print '    curEv  % .5e' % (curEv)
        MoveInfo = dict(didAccept=0,
                        kA=kA,
                        kB=kB,
                        msg="CRAP. bad proposed evidence.")
        return curModel, SS, curEv, MoveInfo

    if hasattr(SS, 'nDoc') and (propEv > 0 and curEv < 0):
        print 'CRAP! ---------------------------------------!!!!@@@@@@@@'
        print '    propEv % .5e' % (propEv)
        print '    curEv  % .5e' % (curEv)
        MoveInfo = dict(didAccept=0,
                        kA=kA,
                        kB=kB,
                        msg="CRAP. bad proposed evidence.")
        return curModel, SS, curEv, MoveInfo

    if propEv >= curEv:
        MSelector.reindexAfterMerge(kA, kB)
        msg = "merge %3d & %3d | ev +%.3e ****" % (kA, kB, propEv - curEv)
        MoveInfo = dict(didAccept=1, kA=kA, kB=kB, msg=msg, evDiff=evDiff)
        if doWriteLog:
            log_merge_move(MoveInfo, MSelector, curModel, SS, savedir)
        return propModel, propSS, propEv, MoveInfo
    else:
        msg = "merge %3d & %3d | ev -%.3e" % (kA, kB, curEv - propEv)
        MoveInfo = dict(didAccept=0, kA=kA, kB=kB, msg=msg, evDiff=evDiff)
        if doWriteLog:
            log_merge_move(MoveInfo, MSelector, curModel, SS, savedir)
        return curModel, SS, curEv, MoveInfo