hvRecursive: boolean comparison of np.array to None

[Corwinpro]

Steps to reproduce

Please see the following snippet:

import nevergrad as ng
from nevergrad.functions import MultiobjectiveFunction

SIZE = 2

def multiobjective(*args, **kwargs):
    return [1] * SIZE

f = MultiobjectiveFunction(
    multiobjective_function=multiobjective, upper_bounds=[5] * SIZE
)

optimizer = ng.optimizers.OnePlusOne(instrumentation=1, budget=100)
recommendation = optimizer.minimize(f)
print(recommendation)

Change SIZE from 2 to 3 to observe the problem.

Observed Results

• The example above results in ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all().
• The problem is in nevergrad/functions/multiobjective/pyhv.py:127:

          while q.cargo != None:

This apparently should be

            while q.cargo is not None:

• It feels that with SIZE == 2 the _HyperVolume().hvRecursive is never called. With SIZE > 2 it is called, and therefore throws the error.

Expected Results

It is up to the developers to decide what comparison it should be there, element-wise or array to None.

Relevant Code

Please see above.

Suggestions

Change the comparison in while loop to while q.cargo is not None:. This fixed the problem to me, although I don't know whether we want to do .any() or .all() instead.

Thank you.

[Corwinpro]

This issue is approached by #356

[Corwinpro]

Fixed in #356.