def linear_update(xs, ws, y, ep):
""" Update rules for linear ANNs using the delta rule,
i.e., delta = ep * (xs (h - y)), where h is hypothesis/activation
(from annclass.activation.linear()).
Note: in multilayer ANN an average of two good weights may be a bad
set of weights, i.e. they are not convex. Unlike perceptrons, whose
weights are proven to reach a 'good' set of weights, linear (or multilayer)
ANNs are proven instead to have their predictions approach the target. Also
note that perceptrons are not proven to have their predictions approach the
target, yet somehow the weights are known-good. An odd state of affairs.
FYI, Linear neurons are linear filters in EE (with ep being the severity
of filtration). For linear cases and squared error functions there are of
course analytical solutions for the update rather than the
iterative procedure used here (e.g. OLS). Iterative methods are used
so non-linear functions and non-squared error functions can be used,
and to better mimic the brain.
"""
h = linear(xs, ws, None)
delta_w = delta(xs, y, h, ep) ## delta loss function
ws_new = ws + delta_w
# Return the new wieghts and the new guess.
return ws_new, linear(xs, ws_new, None)
def print_linear_update(xs, ws, bias, y, ep):
""" Prints initial and updated ws, and h. """
# Convert xs ans ws to the proper form
# for use in perceptron
xs = np.array(xs)
ws = np.array(ws)
# Not using setup_bias so do this by hand.
h = linear(xs, ws, None) ## The inital hypothesis
ws_new, h_new = linear_update(xs, ws, y, ep)
print("ws_intial: {0}\nws_new: {1}".format(ws, ws_new))
print("h_intial: {0}\nh_new: {1}".format(h,h_new))
