why does it warn me no forces provide torque while the active force torque works?

[lucasda42]

I keep getting the warning ;" Warning: Requested integration of orientations, but no forces provide torques."
While the torque of the active force does get applied, is something wrong with my code or why does it tell me this?

import gsd.hoomd
import hoomd

Create starting frame

frame = gsd.hoomd.Frame()
frame.particles.N = 1
frame.particles.position = [(0,-1,0)]
frame.configuration.box = [3, 3, 0, 0, 0, 0]
frame.particles.moment_inertia=[(0,0,1)]
frame.particles.types = ['A']

Set up simulation environment

cpu = hoomd.device.CPU()
sim = hoomd.Simulation(device=cpu, seed=2)
sim.create_state_from_snapshot(frame)

#Define integrator
integrator = hoomd.md.Integrator(dt=0.1,integrate_rotational_dof=True)

#Define active force and torque
active = hoomd.md.force.Active(filter=hoomd.filter.All())
active.active_force['A'] = (1, 0, 0)
active.active_torque['A'] = (0,0,1)

#Add active
integrator.forces.append(active)

#Define brownian method
brownian = hoomd.md.methods.Brownian(kT=0, filter=hoomd.filter.All())
integrator.methods.append(brownian)

#Set sims integrator
sim.operations.integrator = integrator

define and add writer

gsd_writer = hoomd.write.GSD(filename='test-minimal.gsd', trigger=hoomd.trigger.Periodic(1), mode='wb')
sim.operations.writers.append(gsd_writer)

sim.run(63)

gsd_writer.flush()

[joaander]

The warning is printed by IntegratorTwoStep,

hoomd-blue/hoomd/md/IntegratorTwoStep.cc

Lines 229 to 234 in 41af37e

	if (m_integrate_rotational_dof && !areForcesAnisotropic())
	{
	m_exec_conf->msg->warning() << "Requested integration of orientations, but no forces"
	" provide torques."
	<< endl;
	}

areForcesAnisotropic calls isAnisotropic() on every force,

hoomd-blue/hoomd/Integrator.cc

Lines 861 to 864 in 41af37e

	for (const auto& force : m_forces)
	{
	aniso |= force->isAnisotropic();
	}

ActiveForceCompute fails to override isAnisotropic(), and the default is false:

hoomd-blue/hoomd/ForceCompute.h

Lines 170 to 174 in 41af37e

	virtual bool isAnisotropic()
	{
	// by default, only translational degrees of freedom are integrated
	return false;
	}

To prevent this warning in future HOOMD-blue releases, you should make a pull request that overrides isAnisotropic in hoomd/md/ActiveForceCompute.h with return true.