Source code for anneal.anneal

'''Main module for anneal.

This module contains the main (and only, by now) function of anneal:

import time

__all__ = ['simulated_annealing']

[docs]def simulated_annealing(P, ID, beta_min=1e-2, beta_max=1e2, cooling_rate=1e-2, n_steps_per_T=100, E_min=-float('inf'), quench_to_T0=False, n_steps_T0=1000): ''' General-purpose simulated-annealing optimization function. Parameters ---------- P : object Instance of a custom class, wich includes attributes + P.beta + and methods: + P.set_beta(beta) + P.MC_move(), returning 1/0 (accepted/rejected) + P.update_MC_parameters(acc_ratio) ID : str Label for the problem under study. beta_min : float, optional Minimum inverse temperature (default: 1e-2) beta_max: float, optional Maximum inverse temperature (default: 1e2) cooling_rate : float, optional Cooling rate (default: 1e-2) n_steps_per_T : int, optional Number of MC moves attempted at each temperature (default: 100) E_min : float, optional Global energy minimum, if known (default: -infinity) quench_to_T0 : bool, optional If True, perform a T=0 quench at the end of the annealing n_steps_T0 : int, optional Number of MC moves after the T=0 quench Returns ------- P : object Current version of P E : list List of the final energies for each temperature elapsed_time : float Total elapsed time, in seconds ''' # initialize time_start = time.clock() P.set_beta(beta_min) E = [] out = open('log_sim_ann_%s.dat' % ID, 'w') out.write('# start - %s\n' % time.strftime('%c')) out.write('# beta_min: %f\n' % beta_min) out.write('# beta_max: %f\n' % beta_max) out.write('# cooling rate: %f\n' % cooling_rate) out.write('# n_steps_per_T %f\n' % n_steps_per_T) out.write('# initial energy: %f\n' % out.write('# quench_to_T0: %s\n' % quench_to_T0) out.write('# n_steps_T0: %i\n' % n_steps_T0) out.write('#\n') out.flush() # annealing loop while P.beta < beta_max: acc = 0 for step in range(n_steps_per_T): acc += P.MC_move() acc_ratio = acc / float(n_steps_per_T) out.write('%10.4g %10.4g %.8f\n' % (P.beta,, acc_ratio)) out.flush() E.append( if <= E_min: out.write('# reached E_min=%s. Break.\n' % E_min) out.flush() break # update beta and MC parameters P.set_beta(P.beta * (1.0 + cooling_rate)) P.update_MC_parameters(acc_ratio) # T=0 quench if quench_to_T0: out.write('# start T=0 quench\n') out.flush() P.set_beta(1e24) for step in range(n_steps_T0): P.MC_move() E.append( out.write('# %12.4g %10.4g %.8f\n' % (P.beta,, acc_ratio)) out.write('# after quench, reached E=%g\n' % out.flush() # finalize out.write('# end\n') elapsed_time = time.clock() - time_start out.write('# elapsed: %.2f s\n' % elapsed_time) out.close() return P, E, elapsed_time