from pylab import *

import cv2 as cv

#==============================================================================

# Some parameters for learning.  Step size is the gradient step size

# for backpropogation.

step_size = 0.01

# Momentum can be ignored for this example.

momentum = 0.0

# Max steps of training

nsteps = 10000

# Error threshold for halting training

max_err = 0.0001

# When to stop: whichever comes first, count or error

condition = cv.TERM_CRITERIA_COUNT | cv.TERM_CRITERIA_EPS

# Tuple of termination criteria: first condition, then # steps, then

# error tolerance second and third things are ignored if not implied

# by condition

criteria = (condition, nsteps, max_err)

# params is a dictionary with relevant things for NNet training.

params = dict( term_crit = criteria, 

               train_method = cv.ANN_MLP_TRAIN_PARAMS_BACKPROP, 

               bp_dw_scale = step_size, 

               bp_moment_scale = momentum )

#==============================================================================

layer_sizes = array([1,52,2])

mlp = cv.ANN_MLP(layer_sizes)

# create an input vector x, and an output vector y

x = linspace(0,1)       # x is one-dimensional

y1 = (sin(x*2*pi)+1)/2. # y is two-dimensional

y2 = (cos(x*2*pi)+1)/2.

y = hstack((y1.reshape(-1,1),y2.reshape(-1,1)))

#z = array(zeros_like(y),order='c')+.5   # z catches output from ANN_MLP(train)

z = zeros_like(y)+.5    # when z isn't forced to be C-contiguous, something fails between numpy and C

# show that z is Fortran contiguous, rather than C contiguous

print "Notice that z is Fortran contiguous, rather than C contiguous:"

print z.flags

print "When performing a lot of vstack and hstack operations, for"

print "efficiency reasons, sometimes Numpy will switch continuity."

# make the input and output larger

inpt = x

inpt = hstack((inpt,inpt))

inpt = hstack((inpt,inpt))

inpt = hstack((inpt,inpt))

outpt = y

outpt = vstack((outpt,outpt))

outpt = vstack((outpt,outpt))

outpt = vstack((outpt,outpt))

# train and predict

mlp.train(inpt,outpt,None,params=params)

mlp.predict(x,z)

# plot an idealization of the training set as a solid line

# and the output of the neural network as dots

figure()

title("first dimension of training data\n (dots should line up on the sine curve)")

plot(x,y[:,0],'b')

plot(x,z[:,0],'go')

# plot an idealization of the training set as a solid line

# and the output of the neural network as dots

figure()

title("second dimension of training data\n (dots should line up on the cosine curve)")

plot(x,y[:,1],'r')

plot(x,z[:,1],'yo')

show()