PowStep device based on Fusi & Abott synapse model

[maljoras]

Related issues

#181

Description

Implements a new device model class (PowStepDevice) based on Fusi & Abott (2007).

Example:

import matplotlib.pyplot as plt
from aihwkit.utils.visualization import plot_device_compact
from aihwkit.simulator.configs.devices import PowStepDevice

plt.ion()
plot_device_compact(
    PowStepDevice(w_min=-1, w_max=1, dw_min=0.01, pow_gamma=1.1, pow_gamma_dtod=0.5,
                  pow_up_down=0.2, w_min_dtod=0.0, w_max_dtod=0.0), n_steps=1000)
plt.show()

[diego-plan9]

Nice!

[diego-plan9]

Thanks! I added a commit merging the changes from master (as a couple of small conflicts were introduced after merging #191 ), and should be good to go.