def test_drift_weights(self):
"""Check drifting the weights."""
nu = 0.1
drift_params = DriftParameter(nu=nu, t_0=1.0, nu_dtod=0.0, nu_std=0.0, w_noise_std=0.0)
delta_t = 2.0
# Use custom parameters for the tile.
python_tile = self.get_custom_tile(100, 122, drift=drift_params)
cpp_tile = python_tile.tile
init_weights = cpp_tile.get_weights().copy()
cpp_tile.drift_weights(delta_t)
weights = cpp_tile.get_weights()
assert_array_almost_equal(weights, init_weights*(delta_t)**(-nu))
class PulsedDevice(_PrintableMixin):
r"""Pulsed update resistive devices.
Device are used as part of an
:class:`~aihwkit.simulator.tiles.AnalogTile` to implement the
`update once` characteristics, i.e. the material response properties
when a single update pulse is given (a coincidence between row and
column pulse train happened).
Common properties of all pulsed devices include:
**Reset**:
Resets the weight in cross points to (around) zero with
cycle-to-cycle and systematic spread around a mean.
Important:
Reset with given parameters is only activated when
:meth:`~aihwkit.simulator.tiles.base.Base.reset_weights` is
called explicitly by the user.
**Decay**:
.. math:: w_{ij} \leftarrow w_{ij}\,(1-\alpha_\text{decay}\delta_{ij})
Weight decay is only activated by inserting a specific call to
:meth:`~aihwkit.simulator.tiles.base.Base.decay_weights`, which is
done automatically for a tile each mini-batch is decay is
present. Note that the device ``decay_lifetime`` parameters (1
over decay rates :math:`\delta_{ij}`) are analog tile specific and
are thus set and fixed during RPU
initialization. :math:`\alpha_\text{decay}` is a scaling factor
that can be given during run-time.
**Diffusion**:
Similar to the decay, diffusion is only activated by inserting a
specific call to
:meth:`~aihwkit.simulator.tiles.base.Base.diffuse_weights`, which is
done automatically for a tile each mini-batch is diffusion is
present. The parameters of the diffusion process are set during
RPU initialization and are fixed for the remainder.
.. math:: w_{ij} \leftarrow w_{ij} + \rho_{ij} \, \xi;
where :math:`xi` is a standard Gaussian variable and :math:`\rho_{ij}` the
diffusion rate for a cross-point `ij`.
Note:
If diffusion happens to move the weight beyond the hard bounds of the
weight it is ensured to be clipped appropriately.
**Drift**:
Optional power-law drift setting, as described in
:class:`~aihwkit.similar.configs.utils.DriftParameter`.
Important:
Similar to reset, drift is *not* applied automatically each
mini-batch but requires an explicit call to
:meth:`~aihwkit.simulator.tiles.base.Base.drift_weights` each
time the drift should be applied.
"""
bindings_class: ClassVar[Type] = devices.PulsedResistiveDeviceParameter
construction_seed: int = 0
"""If not equal 0, will set a unique seed for hidden parameters during
construction."""
corrupt_devices_prob: float = 0.0
"""Probability for devices to be corrupt (weights fixed to random value
with hard bounds, that is min and max bounds are set to equal)."""
corrupt_devices_range: int = 1000
"""Range around zero for establishing corrupt devices."""
diffusion: float = 0.0
"""Standard deviation of diffusion process."""
diffusion_dtod: float = 0.0
"""Device-to device variation of diffusion rate in relative units."""
drift: DriftParameter = field(default_factory=DriftParameter,
metadata={'hide_if': DriftParameter()})
"""Parameter governing a power-law drift."""
dw_min: float = 0.001
"""Mean of the minimal update step sizes across devices and directions."""
dw_min_dtod: float = 0.3
"""Device-to-device std deviation of dw_min (in relative units to
``dw_min``)."""
dw_min_std: float = 0.3
r"""Cycle-to-cycle variation size of the update step (related to
:math:`\sigma_\text{c-to-c}` above) in relative units to ``dw_min``.
Note:
Many spread (device-to-device variation) parameters are given in
relative units. For instance e.g. a setting of ``dw_min_std`` of 0.1
would mean 10% spread around the mean and thus a resulting standard
deviation (:math:`\sigma_\text{c-to-c}`) of ``dw_min`` * ``dw_min_std``.
"""
enforce_consistency: bool = True
"""Whether to enforce weight bounds consistency during initialization.
Whether to enforce that max weight bounds cannot be smaller than min
weight bounds, and up direction step size is positive and down negative.
Switches the opposite values if encountered during init.
"""
lifetime: float = 0.0
r"""One over `decay_rate`, ie :math:`1/r_\text{decay}`."""
lifetime_dtod: float = 0.0
"""Device-to-device variation in the decay rate (in relative units)."""
perfect_bias: bool = False
"""No up-down differences and device-to-device variability in the bounds
for the devices in the bias row."""
reset: float = 0.01
"""The reset values and spread per cross-point ``ij`` when using reset
functionality of the device."""
reset_dtod: float = 0.0
"""See ``reset``."""
reset_std: float = 0.01
"""See ``reset``."""
up_down: float = 0.0
r"""Up and down direction step sizes can be systematically different and
also vary across devices.
:math:`\Delta w_{ij}^d` is set during RPU initialization (for each
cross-point :math:`ij`):
.. math::
\Delta w_{ij}^d = d\; \Delta w_\text{min}\, \left(
1 + d \beta_{ij} + \sigma_\text{d-to-d}\xi\right)
where :math:`\xi` is again a standard Gaussian. :math:`\beta_{ij}` is the
directional up `versus` down bias. At initialization ``up_down_dtod`` and
``up_down`` defines this bias term:
.. math::
\beta_{ij} = \beta_\text{up-down} + \xi
\sigma_\text{up-down-dtod}
where :math:`\xi` is again a standard Gaussian number and
:math:`\beta_\text{up-down}` corresponds to ``up_down``. Note that
``up_down_dtod`` is again given in relative units to ``dw_min``.
"""
up_down_dtod: float = 0.01
"""See ``up_down``."""
w_max: float = 0.6
"""See ``w_min``."""
w_max_dtod: float = 0.3
"""See ``w_min_dtod``."""
w_min: float = -0.6
"""Mean of hard bounds across device cross-point `ij`.
The parameters ``w_min`` and ``w_max`` are used to set the min/max bounds
independently.
Note:
For this abstract device, we assume that weights can have
positive and negative values and are symmetrically around
zero. In physical circuit terms, this might be implemented
as a difference of two resistive elements.
"""
w_min_dtod: float = 0.3
"""Device-to-device variation of the hard bounds.
Device-to-device variation of the hard bounds, of min and max value,
respectively. All are given in relative units to ``w_min``, or ``w_max``,
respectively.
"""
def as_bindings(self) -> devices.PulsedResistiveDeviceParameter:
"""Return a representation of this instance as a simulator bindings object."""
return parameters_to_bindings(self)
def requires_diffusion(self) -> bool:
"""Return whether device has diffusion enabled."""
return self.diffusion > 0.0
def requires_decay(self) -> bool:
"""Return whether device has decay enabled."""
return self.lifetime > 0.0