qml.pulse.pwc_from_function

pwc_from_function(timespan, num_bins)

Decorates a smooth function, creating a piece-wise constant function that approximates it.

Creates a callable for defining a ParametrizedHamiltonian.

Parameters

• timespan (Union[float, tuple(float)]) – The time span defining the region where the function is non-zero. If a float is provided, the time span is defined as (0, timespan).

• num_bins (int) – number of bins for time-binning the function

Returns

a function that takes some smooth function f(params, t) and converts it to a piece-wise constant function spanning time t in num_bins bins.

Return type

callable

Example

def smooth_function(params, t):
    return params[0] * t + params[1]

timespan = 10
num_bins = 10

binned_function = qml.pulse.pwc_from_function(timespan, num_bins)(smooth_function)

>>> binned_function([2, 4], 3), smooth_function([2, 4], 3)  # t = 3
(Array(10.666667, dtype=float32), 10)

>>> binned_function([2, 4], 3.2), smooth_function([2, 4], 3.2)  # t = 3.2
(Array(10.666667, dtype=float32), 10.4)

>>> binned_function([2, 4], 4.5), smooth_function([2, 4], 4.5)  # t = 4.5
(Array(12.888889, dtype=float32), 13.0)

The same effect can be achieved by decorating the smooth function:

from pennylane.pulse.convenience_functions import pwc_from_function

@pwc_from_function(timespan, num_bins)
def fn(params, t):
    return params[0] * t + params[1]

>>> fn([2, 4], 3)
Array(10.666667, dtype=float32)

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