"""
Clocks for the simulator.
"""
__docformat__ = "restructuredtext en"
import numpy as np
from brian2.core.names import Nameable
from brian2.core.variables import Variables
from brian2.groups.group import VariableOwner
from brian2.units.allunits import second
from brian2.units.fundamentalunits import Quantity, check_units
from brian2.utils.logger import get_logger
__all__ = ["Clock", "defaultclock"]
logger = get_logger(__name__)
[docs]
def check_dt(new_dt, old_dt, target_t):
"""
Check that the target time can be represented equally well with the new
dt.
Parameters
----------
new_dt : float
The new dt value
old_dt : float
The old dt value
target_t : float
The target time
Raises
------
ValueError
If using the new dt value would lead to a difference in the target
time of more than `Clock.epsilon_dt` times ``new_dt`` (by default,
0.01% of the new dt).
Examples
--------
>>> from brian2 import *
>>> check_dt(float(17*ms), float(0.1*ms), float(0*ms)) # For t=0s, every dt is fine
>>> check_dt(float(0.05*ms), float(0.1*ms), float(10*ms)) # t=10*ms can be represented with the new dt
>>> check_dt(float(0.2*ms), float(0.1*ms), float(10.1*ms)) # t=10.1ms cannot be represented with dt=0.2ms # doctest: +ELLIPSIS
Traceback (most recent call last):
...
ValueError: Cannot set dt from 100. us to 200. us, the time 10.1 ms is not a multiple of 200. us.
"""
old_t = np.int64(np.round(target_t / old_dt)) * old_dt
new_t = np.int64(np.round(target_t / new_dt)) * new_dt
error_t = target_t
if abs(new_t - old_t) / new_dt > Clock.epsilon_dt:
old = str(old_dt * second)
new = str(new_dt * second)
t = str(error_t * second)
raise ValueError(
f"Cannot set dt from {old} to {new}, the "
f"time {t} is not a multiple of {new}."
)
[docs]
class Clock(VariableOwner):
"""
An object that holds the simulation time and the time step.
Parameters
----------
dt : float
The time step of the simulation as a float
name : str, optional
An explicit name, if not specified gives an automatically generated name
Notes
-----
Clocks are run in the same `Network.run` iteration if `~Clock.t` is the
same. The condition for two
clocks to be considered as having the same time is
``abs(t1-t2)<epsilon*abs(t1)``, a standard test for equality of floating
point values. The value of ``epsilon`` is ``1e-14``.
"""
def __init__(self, dt, name="clock*"):
# We need a name right away because some devices (e.g. cpp_standalone)
# need a name for the object when creating the variables
Nameable.__init__(self, name=name)
self._old_dt = None
self.variables = Variables(self)
self.variables.add_array(
"timestep", size=1, dtype=np.int64, read_only=True, scalar=True
)
self.variables.add_array(
"t",
dimensions=second.dim,
size=1,
dtype=np.float64,
read_only=True,
scalar=True,
)
self.variables.add_array(
"dt",
dimensions=second.dim,
size=1,
values=float(dt),
dtype=np.float64,
read_only=True,
constant=True,
scalar=True,
)
self.variables.add_constant("N", value=1)
self._enable_group_attributes()
self.dt = dt
logger.diagnostic(f"Created clock {self.name} with dt={self.dt}")
@check_units(t=second)
def _set_t_update_dt(self, target_t=0 * second):
new_dt = self.dt_
old_dt = self._old_dt
target_t = float(target_t)
if old_dt is not None and new_dt != old_dt:
self._old_dt = None
# Only allow a new dt which allows to correctly set the new time step
check_dt(new_dt, old_dt, target_t)
new_timestep = self._calc_timestep(target_t)
# Since these attributes are read-only for normal users, we have to
# update them via the variables object directly
self.variables["timestep"].set_value(new_timestep)
self.variables["t"].set_value(new_timestep * new_dt)
logger.diagnostic(f"Setting Clock {self.name} to t={self.t}, dt={self.dt}")
def _calc_timestep(self, target_t):
"""
Calculate the integer time step for the target time. If it cannot be
exactly represented (up to 0.01% of dt), round up.
Parameters
----------
target_t : float
The target time in seconds
Returns
-------
timestep : int
The target time in integers (based on dt)
"""
new_i = np.int64(np.round(target_t / self.dt_))
new_t = new_i * self.dt_
if new_t == target_t or np.abs(new_t - target_t) / self.dt_ <= Clock.epsilon_dt:
new_timestep = new_i
else:
new_timestep = np.int64(np.ceil(target_t / self.dt_))
return new_timestep
def __repr__(self):
return f"Clock(dt={self.dt!r}, name={self.name!r})"
def _get_dt_(self):
return self.variables["dt"].get_value().item()
@check_units(dt_=1)
def _set_dt_(self, dt_):
self._old_dt = self._get_dt_()
self.variables["dt"].set_value(dt_)
@check_units(dt=second)
def _set_dt(self, dt):
self._set_dt_(float(dt))
dt = property(
fget=lambda self: Quantity(self.dt_, dim=second.dim),
fset=_set_dt,
doc="""The time step of the simulation in seconds.""",
)
dt_ = property(
fget=_get_dt_,
fset=_set_dt_,
doc="""The time step of the simulation as a float (in seconds)""",
)
@check_units(start=second, end=second)
def set_interval(self, start, end):
"""
set_interval(self, start, end)
Set the start and end time of the simulation.
Sets the start and end value of the clock precisely if
possible (using epsilon) or rounding up if not. This assures that
multiple calls to `Network.run` will not re-run the same time step.
"""
self._set_t_update_dt(target_t=start)
end = float(end)
self._i_end = self._calc_timestep(end)
if self._i_end > 2**40:
logger.warn(
"The end time of the simulation has been set to "
f"{str(end*second)}, which based on the dt value of "
f"{str(self.dt)} means that {self._i_end} "
"time steps will be simulated. This can lead to "
"numerical problems, e.g. the times t will not "
"correspond to exact multiples of "
"dt.",
"many_timesteps",
)
#: The relative difference for times (in terms of dt) so that they are
#: considered identical.
epsilon_dt = 1e-4
[docs]
class DefaultClockProxy:
"""
Method proxy to access the defaultclock of the currently active device
"""
def __getattr__(self, name):
if name == "_is_proxy":
return True
from brian2.devices.device import active_device
return getattr(active_device.defaultclock, name)
def __setattr__(self, key, value):
from brian2.devices.device import active_device
setattr(active_device.defaultclock, key, value)
#: The standard clock, used for objects that do not specify any clock or dt
defaultclock = DefaultClockProxy()