Serialization problem on multi-objective optimization in archipelagos [sf#8]

[darioizzo]

Originally created by mmarcusx on 2012-10-23 15:46:20.

Evolution on a specific problem makes the archipelago crash.

To reproduce: download the problem from the attachment and then try:

from PyGMO import *
import dtlz4 as dt4
alg = algorithm.nsga_II(gen=1)
archi = archipelago()
archi.push_back(island(alg, dt4.dtlz4(restrict=[1,2]), 12))

archi.evolve(400)
archi[0]

(If you do not see the error, try another archi.evolve(400))

Stepping inside with pdb and checking state[1] reveals "-nan" values in the middle of all these numbers.

These -nans are somehow correlated to nans produced in population.cpp, in the method "update_crowding_d":

double df = get_individual(I[lastidx]).cur_f[i] - get_individual(I[0]).cur_f[i];
m_crowding_d[I[j]] += (get_individual(I[j+1]).cur_f[i] - get_individual(I[j-1]).cur_f[i])/df;

As with this particular problem, all individuals converge to one point, the border solutions are identical and thus df == 0.0

In the branch "development_marcus" is a workaround for the crowding distance implemented.

It is still unclear, why this bug is causing the archipelago to crash but is not reproducible by using a single island only. Moreover, the method in serialization.h to catch nans and infs seems not to work as we are dealing with negative nans here.

[darioizzo]

Originally posted by mmarcusx on 2013-03-11 16:02:10.

• status: open --> closed

[darioizzo]

Originally posted by mmarcusx on 2013-03-11 16:02:11.

Negative -nans no longer occur in the computation of the crowding distance. Bug fixed.