@cleardusk 2015-11-13T08:59:54.000000Z 字数 3369 阅读 1313

# BP

GjzCVCode

# Back-Propagation Neural Networks# # Written in Python.  See http://www.python.org/# Placed in the public domain.# Neil Schemenauer <nas@arctrix.com>import mathimport randomimport stringrandom.seed(0)# calculate a random number where:  a <= rand < bdef rand(a, b):    return (b-a)*random.random() + a# Make a matrix (we could use NumPy to speed this up)def makeMatrix(I, J, fill=0.0):    m = []    for i in range(I):        m.append([fill]*J)    return m# our sigmoid function, tanh is a little nicer than the standard 1/(1+e^-x)def sigmoid(x):    return math.tanh(x) # this is not sigmoid function, but it's effect is better    # return 1.0/(math.exp(-x)+1.0) # this is really sigmoid function# derivative of our sigmoid function, in terms of the output (i.e. y)def dsigmoid(y):    return 1.0 - y**2 # tanh    # return y - y**2 # sigmoidclass NN:    def __init__(self, ni, nh, no):        # number of input, hidden, and output nodes        self.ni = ni + 1 # +1 for bias node        self.nh = nh        self.no = no        # activations for nodes        self.ai = [1.0]*self.ni        self.ah = [1.0]*self.nh        self.ao = [1.0]*self.no        # create weights        self.wi = makeMatrix(self.ni, self.nh)        self.wo = makeMatrix(self.nh, self.no)        # set them to random vaules        for i in range(self.ni):            for j in range(self.nh):                self.wi[i][j] = rand(-0.2, 0.2)        for j in range(self.nh):            for k in range(self.no):                self.wo[j][k] = rand(-2.0, 2.0)        # last change in weights for momentum           self.ci = makeMatrix(self.ni, self.nh)        self.co = makeMatrix(self.nh, self.no)    def update(self, inputs):        if len(inputs) != self.ni-1:            raise ValueError('wrong number of inputs')        # input activations        for i in range(self.ni-1):            #self.ai[i] = sigmoid(inputs[i])            self.ai[i] = inputs[i]        # hidden activations        for j in range(self.nh):            sum = 0.0            for i in range(self.ni):                sum = sum + self.ai[i] * self.wi[i][j]            self.ah[j] = sigmoid(sum)        # output activations        for k in range(self.no):            sum = 0.0            for j in range(self.nh):                sum = sum + self.ah[j] * self.wo[j][k]            self.ao[k] = sigmoid(sum)        return self.ao[:]    def backPropagate(self, targets, N, M):        if len(targets) != self.no:            raise ValueError('wrong number of target values')        # calculate error terms for output        output_deltas = [0.0] * self.no        for k in range(self.no):            error = targets[k]-self.ao[k]            output_deltas[k] = dsigmoid(self.ao[k]) * error        # calculate error terms for hidden        hidden_deltas = [0.0] * self.nh        for j in range(self.nh):            error = 0.0            for k in range(self.no):                error = error + output_deltas[k]*self.wo[j][k]            hidden_deltas[j] = dsigmoid(self.ah[j]) * error        # update output weights        for j in range(self.nh):            for k in range(self.no):                change = output_deltas[k]*self.ah[j]                # self.wo[j][k] = self.wo[j][k] + N*change + M*self.co[j][k]                self.wo[j][k] = self.wo[j][k] + N*change                self.co[j][k] = change                #print N*change, M*self.co[j][k]        # update input weights        for i in range(self.ni):            for j in range(self.nh):                change = hidden_deltas[j]*self.ai[i]                # self.wi[i][j] = self.wi[i][j] + N*change + M*self.ci[i][j]                self.wi[i][j] = self.wi[i][j] + N*change                self.ci[i][j] = change        # calculate error        error = 0.0        for k in range(len(targets)):            error = error + 0.5*(targets[k]-self.ao[k])**2        return error    def test(self, patterns):        for p in patterns:            print(p[0], '->', self.update(p[0]))    def weights(self):        print('Input weights:')        for i in range(self.ni):            print(self.wi[i])        print()        print('Output weights:')        for j in range(self.nh):            print(self.wo[j])    def train(self, patterns, iterations=1000, N=0.5, M=0.1):        # N: learning rate        # M: momentum factor        for i in range(iterations):            error = 0.0            for p in patterns:                inputs = p[0]                targets = p[1]                self.update(inputs)                error = error + self.backPropagate(targets, N, M)            if i % 100 == 0:                print('error %-.5f' % error)def demo():    # Teach network XOR function    pat = [        [[0,0], [0]],        [[0,1], [1]],        [[1,0], [1]],        [[1,1], [0]]    ]    # create a network with two input, two hidden, and one output nodes    n = NN(2, 2, 1)    # train it with some patterns    n.train(pat)    # test it    n.test(pat)if __name__ == '__main__':    demo()

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