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# fmt: off
import numpy as np
from ase.build import molecule
from ase.constraints import FixedMode, dict2constraint
def test_fixedmode():
"""Test that FixedMode can be set, turned into a dict, and
back to a constraint with the same mode."""
# Create a simple mode.
atoms = molecule('CH3OH')
initial_positions = atoms.positions.copy()
atoms.rattle(stdev=0.5)
mode = atoms.positions - initial_positions
# Test the constraint.
constraint = FixedMode(mode)
dict_constraint = constraint.todict()
new_constraint = dict2constraint(dict_constraint)
assert np.isclose(new_constraint.mode, constraint.mode).all()
atoms.set_constraint(constraint)
assert atoms.get_number_of_degrees_of_freedom() == 2 * len(atoms)
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