Replica.py

# replica exchange class
# inspired by ISD Replica.py
# Yannick

from __future__ import print_function, division
import numpy as np
from numpy.random import random, randint
kB = 1.3806503 * 6.0221415 / 4184.0  # Boltzmann constant in kcal/mol/K


class ReplicaTracker:

    def __init__(self, nreps, inv_temps, grid, sfo_id,
                 rexlog='replicanums.txt', scheme='standard', xchg='random',
                 convectivelog='stirred.txt', tune_temps=False,
                 tune_data={}, templog='temps.txt'):
        self.nreps = nreps
        # replica number as a function of state no
        self.replicanums = list(range(nreps))
        # state no as a function of replica no
        self.statenums = list(range(nreps))
        self.grid = grid
        self.sfo_id = sfo_id
        # expect inverse temperatures
        self.inv_temps = inv_temps
        self.logfile = rexlog
        self.stepno = 1
        self.scheme = scheme
        self.xchg = xchg
        self.tune_temps = tune_temps
        self.tune_data = tune_data
        self.rn_history = []
        self.templog = templog
        # scheme is one of gromacs, randomneighbors or convective
        if scheme == "convective":
            self.stirred = {}
            # which order the replicas should be chosen
            self.stirred['order'] = list(range(self.nreps))
            self.stirred['order'].reverse()
            # which replica is currently being stirred
            self.stirred['replica'] = self.stirred['order'][0]
            # which position in the order list this replica sits in
            self.stirred['pos'] = 0
            # what direction should this replica should go to
            if self.stirred['replica'] != self.nreps - 1:
                self.stirred['dir'] = 1  # up
            else:
                self.stirred['dir'] = 0  # down
            # how many steps are remaining til we change stirring replica
            self.stirred['steps'] = 2 * (self.nreps - 1)
            self.convectivelog = convectivelog
        self.write_rex_stats()

    def sort_per_state(self, inplist):
        "sorts a replica list per state"
        if len(inplist) != self.nreps:
            raise ValueError('list has wrong size')
        return [inplist[i] for i in self.replicanums]

    def sort_per_replica(self, inplist):
        "sorts a state list per replica number"
        if len(inplist) != self.nreps:
            raise ValueError('list has wrong size')
        return [inplist[i] for i in self.statenums]

    def get_energies(self):
        "return replica-sorted energies"
        return self.grid.gather(
            self.grid.broadcast(self.sfo_id, 'm', 'evaluate', False))

    def gen_pairs_list_gromacs(self, direction):
        """generate ordered list of exchange pairs based on direction.
        direction == 0 : (0,1)(2,3)...
        direction == 1 : (0(1,2)(3,4)...
        returns only pairs.
        """
        nreps = self.nreps
        if direction != 0 and direction != 1:
            raise ValueError(direction)
        if nreps == 2:
            return [(0, 1)]
        ret = [(2 * i + direction, 2 * i + 1 + direction)
               for i in range(nreps // 2)]
        if nreps in ret[-1]:
            ret.pop()
        return ret

    def gen_pairs_list_rand(self, needed=[]):
        "generate list of neighboring pairs of states"
        nreps = self.nreps
        pairslist = []
        # generate all possible pairs
        init = [(i, i + 1) for i in range(nreps - 1)]
        # add this pair to form a loop
        init.append((0, nreps - 1))
        # add needed pairs and remove overlapping candidates
        for (i, j) in needed:
            if j - i != 1:
                raise ValueError("wrong format for 'needed' list")
            pairslist.append((i, i + 1))
            init.remove((i - 1, i))
            init.remove((i, i + 1))
            init.remove((i + 1, i + 2))
        while len(init) > 0:
            # choose random pair
            i = randint(0, len(init))  # numpy randint is [a,b[
            # remove it from list
            pair = init.pop(i)
            # print pair
            # remove overlapping
            init = [(r, q) for (r, q) in init
                    if (r not in pair and q not in pair)]
            # print init
            # add to pairslist
            if not pair == (0, nreps - 1):
                pairslist.append(pair)
        # print "pl:",sorted(pairslist)
        pairslist.sort()
        return pairslist

    def gen_pairs_list_conv(self):
        rep = self.stirred['replica']
        state = self.statenums[rep]
        pair = sorted([state, state + 2 * self.stirred['dir'] - 1])
        self.stirred['pair'] = tuple(pair)
        if self.xchg == 'gromacs':
            dir = (state + 1 + self.stirred['dir']) % 2
            return self.gen_pairs_list_gromacs(dir)
        elif self.xchg == 'random':
            return self.gen_pairs_list_rand(needed=[self.stirred['pair']])
        else:
            raise NotImplementedError(
                "Unknown exchange method: %s" %
                self.xchg)

    def gen_pairs_list(self):
        if self.scheme == 'standard':
            if self.xchg == 'gromacs':
                return self.gen_pairs_list_gromacs(self.stepno % 2)
            elif self.xchg == 'random':
                return self.gen_pairs_list_rand()
            else:
                raise NotImplementedError(
                    "unknown exchange method: %s" %
                    self.xchg)
        elif self.scheme == 'convective':
            return self.gen_pairs_list_conv()
        else:
            raise NotImplementedError(
                "unknown exchange scheme: %s" %
                self.scheme)

    def get_cross_energies(self, pairslist):
        "get energies assuming all exchanges have succeeded"
        print("this is not needed for temperature replica-exchange")
        raise NotImplementedError

    def get_metropolis(self, pairslist, old_ene):
        """compute metropolis criterion for temperature replica exchange
        e.g. exp(Delta beta Delta E)
        input: list of pairs, list of state-sorted energies
        """
        metrop = {}
        for (s1, s2) in pairslist:
            metrop[(s1, s2)] = \
                min(1, np.exp((old_ene[s2] - old_ene[s1])
                              * (self.inv_temps[s2] - self.inv_temps[s1])))
        return metrop

    def try_exchanges(self, plist, metrop):
        accepted = []
        for couple in plist:
            if (metrop[couple] >= 1) or (random() < metrop[couple]):
                accepted.append(couple)
        return accepted

    def perform_exchanges(self, accepted):
        "exchange given state couples both in local variables and on the grid"
        # locally
        for (i, j) in accepted:
            # states
            ri = self.replicanums[i]
            rj = self.replicanums[j]
            self.statenums[ri] = j
            self.statenums[rj] = i
            # replicas
            buf = self.replicanums[i]
            self.replicanums[i] = self.replicanums[j]
            self.replicanums[j] = buf
        # on the grid (suboptimal but who cares)
        newtemps = self.sort_per_replica(self.inv_temps)
        states = self.grid.gather(
            self.grid.broadcast(self.sfo_id, 'get_state'))
        for (i, j) in accepted:
            ri = self.replicanums[i]
            rj = self.replicanums[j]
            buf = states[ri]
            states[ri] = states[rj]
            states[rj] = buf
        for temp, state in zip(newtemps, states):
            state['inv_temp'] = temp
        self.grid.gather(
            self.grid.scatter(self.sfo_id, 'set_state', states))

    def write_rex_stats(self):
        "write replica numbers as a function of state"
        fl = open(self.logfile, 'a')
        fl.write('%8d ' % self.stepno)
        fl.write(' '.join(['%2d' % (i + 1) for i in self.replicanums]))
        fl.write('\n')
        fl.close()
        if self.scheme == 'convective':
            fl = open(self.convectivelog, 'a')
            fl.write('%5d ' % self.stepno)
            fl.write('%2d ' % (self.stirred['replica'] + 1))
            fl.write('%2d ' % self.stirred['dir'])
            fl.write('%2d\n' % self.stirred['steps'])
            fl.close()
        if self.tune_temps and len(self.rn_history) == 1:
            fl = open(self.templog, 'a')
            fl.write('%5d ' % self.stepno)
            fl.write(' '.join(['%.3f' % i for i in self.inv_temps]))
            fl.write('\n')
            fl.close()

    def tune_rex(self):
        """use TuneRex to optimize temp set. Temps are optimized every
        'rate' steps and 'method' is used. Data is accumulated as long as
        the temperatures weren't optimized.
        td keys that should be passed to init:
            rate : the rate at which to try tuning temps
            method : flux or ar
            targetAR : for ar only, target acceptance rate
            alpha : Type I error to use.
        """
        import TuneRex
        # update replicanum
        self.rn_history.append([i for i in self.replicanums])
        td = self.tune_data
        if len(self.rn_history) % td['rate'] == 0\
                and len(self.rn_history) > 0:
            temps = [1 / (kB * la) for la in self.inv_temps]
            kwargs = {}
            if td['method'] == 'ar':
                if 'targetAR' in td:
                    kwargs['targetAR'] = td['targetAR']
                if 'alpha' in td:
                    kwargs['alpha'] = td['alpha']
                if 'dumb_scale' in td:
                    kwargs['dumb_scale'] = td['dumb_scale']
                indicators = TuneRex.compute_indicators(
                    np.transpose(self.rn_history))
                changed, newparams = TuneRex.tune_params_ar(
                    indicators, temps, **kwargs)
            elif td['method'] == 'flux':
                if 'alpha' in td:
                    kwargs['alpha'] = td['alpha']
                changed, newparams = TuneRex.tune_params_flux(
                    np.transpose(self.rn_history),
                    temps, **kwargs)
            if changed:
                self.rn_history = []
                print(newparams)
                self.inv_temps = [1 / (kB * t) for t in newparams]

    def do_bookkeeping_before(self):
        self.stepno += 1
        if self.scheme == 'convective':
            st = self.stirred
            # check if we are done stirring this replica
            if st['steps'] == 0:
                st['pos'] = (st['pos'] + 1) % self.nreps
                st['replica'] = st['order'][st['pos']]
                st['dir'] = 1
                st['steps'] = 2 * (self.nreps - 1)
            rep = st['replica']
            state = self.statenums[rep]
            # update endpoints
            if state == self.nreps - 1:
                st['dir'] = 0
            elif state == 0:
                st['dir'] = 1
            self.stirred = st

    def do_bookkeeping_after(self, accepted):
        if self.scheme == 'convective':
            # rep = self.stirred['replica']
            # state = self.statenums[rep]
            # dir = 2 * self.stirred['dir'] - 1
            # expected = (min(state, state + dir), max(state, state + dir))
            if self.stirred['pair'] in accepted:
                self.stirred['steps'] -= 1

    def replica_exchange(self):
        "main entry point for replica-exchange"
        # print "replica exchange"
        self.do_bookkeeping_before()
        # tune temperatures
        if self.tune_temps:
            self.tune_rex()
        # print "energies"
        energies = self.sort_per_state(self.get_energies())
        # print "pairs list"
        plist = self.gen_pairs_list()
        # print "metropolis"
        metrop = self.get_metropolis(plist, energies)
        # print "exchanges"
        accepted = self.try_exchanges(plist, metrop)
        # print "propagate"
        self.perform_exchanges(accepted)
        # print "book"
        self.do_bookkeeping_after(accepted)
        # print "done"