Mercurial > ift6266
annotate baseline/deep_mlp/deepmlp.py @ 572:7ee0e41dd3d5
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author | Yoshua Bengio <bengioy@iro.umontreal.ca> |
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date | Fri, 06 Aug 2010 15:12:01 -0400 |
parents | 89a725d332ae |
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rev | line source |
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1 # |
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2 |
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3 import numpy, cPickle, gzip |
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4 |
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5 |
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6 import theano |
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7 import theano.tensor as T |
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8 |
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9 import time |
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10 |
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11 import theano.tensor.nnet |
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12 |
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13 class MLP(object): |
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14 """Multi-Layer Perceptron Class |
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15 |
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16 A multilayer perceptron is a feedforward artificial neural network model |
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17 that has one layer or more of hidden units and nonlinear activations. |
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18 Intermidiate layers usually have as activation function thanh or the |
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19 sigmoid function while the top layer is a softamx layer. |
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20 """ |
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21 |
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22 |
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23 |
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24 def __init__(self, input, n_in, n_hidden, n_out): |
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25 """Initialize the parameters for the multilayer perceptron |
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26 |
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27 :param input: symbolic variable that describes the input of the |
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28 architecture (one minibatch) |
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29 |
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30 :param n_in: number of input units, the dimension of the space in |
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31 which the datapoints lie |
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32 |
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33 :param n_hidden: List representing the number of units for each |
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34 hidden layer |
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35 |
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36 #:param n_layer: Number of hidden layers |
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37 |
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38 :param n_out: number of output units, the dimension of the space in |
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39 which the labels lie |
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40 |
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41 """ |
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42 |
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43 # initialize the parameters theta = (W,b) ; Here W and b are lists |
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44 # where W[i] and b[i] represent the parameters and the bias vector |
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45 # of the i-th layer. |
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46 n_layer=len(n_hidden) |
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47 W_values=[] |
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48 b_values=[] |
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49 self.W=[] |
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50 self.b=[] |
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51 |
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52 # We first initialize the matrix W[0] and b[0] that represent the parameters |
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53 # from the input to the first hidden layer |
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54 W_values.append(numpy.asarray( numpy.random.uniform( \ |
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55 low = -numpy.sqrt(6./(n_in+n_hidden[0])), \ |
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56 high = numpy.sqrt(6./(n_in+n_hidden[0])), \ |
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57 size = (n_in, n_hidden[0])), dtype = theano.config.floatX)) |
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58 self.W.append(theano.shared( value = W_values[0] )) |
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59 self.b.append(theano.shared( value = numpy.zeros((n_hidden[0],), |
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60 dtype= theano.config.floatX))) |
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61 |
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62 # We initialize the parameters between all consecutive hidden layers |
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63 for i in range(1,n_layer): |
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64 # Each `W[i]` is initialized with `W_values[i]` which is uniformely sampled |
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65 # from -6./sqrt(n_hidden[i]+n_hidden[i+1]) and 6./sqrt(n_hidden[i]+n_hidden[i+1]) |
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66 # the output of uniform if converted using asarray to dtype |
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67 # theano.config.floatX so that the code is runable on GPU |
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68 W_values.append(numpy.asarray( numpy.random.uniform( \ |
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69 low = -numpy.sqrt(6./(n_hidden[i-1]+n_hidden[i])), \ |
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70 high = numpy.sqrt(6./(n_hidden[i-1]+n_hidden[i])), \ |
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71 size = (n_hidden[i-1], n_hidden[i])), dtype = theano.config.floatX)) |
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72 self.W.append(theano.shared( value = W_values[i] )) |
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73 self.b.append(theano.shared( value = numpy.zeros((n_hidden[i],), |
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74 dtype= theano.config.floatX))) |
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75 |
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76 # We initialize the matrix W[n_layer] and b[n_layer] that represent |
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77 # the parameters from the last hidden layer to the output layer using the |
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78 # same uniform sampling. |
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79 W_values.append(numpy.asarray( numpy.random.uniform( |
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80 low = -numpy.sqrt(6./(n_hidden[n_layer-1]+n_out)), \ |
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81 high= numpy.sqrt(6./(n_hidden[n_layer-1]+n_out)),\ |
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82 size= (n_hidden[n_layer-1], n_out)), dtype = theano.config.floatX)) |
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83 self.W.append(theano.shared( value = W_values[n_layer])) |
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84 self.b.append(theano.shared( value = numpy.zeros((n_out,), |
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85 dtype= theano.config.floatX))) |
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86 |
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87 # List of the symbolic expressions computing the values each hidden layer |
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88 self.hidden = [] |
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89 |
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90 # Symbolic expression of the first hidden layer |
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91 self.hidden.append(T.tanh(T.dot(input, self.W[0])+ self.b[0])) |
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92 for i in range(1,n_layer): |
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93 # Symbolic expression of the i-th hidden layer |
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94 self.hidden.append(T.tanh(T.dot(self.hidden[i-1], self.W[i])+ self.b[i])) |
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95 |
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96 # symbolic expression computing the values of the top layer |
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97 self.p_y_given_x= T.nnet.softmax(T.dot(self.hidden[n_layer-1], self.W[n_layer])+self.b[n_layer]) |
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98 |
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99 # compute prediction as class whose probability is maximal in |
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100 # symbolic form |
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101 self.y_pred = T.argmax( self.p_y_given_x, axis =1) |
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102 |
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103 # L1 norm ; one regularization option is to enforce L1 norm to |
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104 # be small |
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105 self.L1=abs(self.W[0]).sum() |
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106 self.L2_sqr=abs(self.W[0]).sum() |
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107 for i in range(1,n_layer+1): |
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108 self.L1 += abs(self.W[i]).sum() |
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109 # square of L2 norm ; one regularization option is to enforce |
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110 # square of L2 norm to be small |
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111 for i in range(n_layer+1): |
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112 self.L2_sqr += abs(self.W[i]**2).sum() |
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113 |
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114 def negative_log_likelihood(self, y): |
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115 return -T.mean(T.log(self.p_y_given_x)[T.arange(y.shape[0]),y]) |
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116 |
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117 def errors(self, y): |
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118 """Return a float representing the number of errors in the minibatch |
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119 over the total number of examples of the minibatch |
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120 """ |
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121 |
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122 # check if y has same dimension of y_pred |
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123 if y.ndim != self.y_pred.ndim: |
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124 raise TypeError('y should have the same shape as self.y_pred', |
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125 ('y', target.type, 'y_pred', self.y_pred.type)) |
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126 # check if y is of the correct datatype |
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127 if y.dtype.startswith('int'): |
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128 # the T.neq operator returns a vector of 0s and 1s, where 1 |
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129 # represents a mistake in prediction |
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130 return T.mean(T.neq(self.y_pred, y)) |
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131 else: |
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132 raise NotImplementedError() |
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133 def sgd_optimization_mnist( learning_rate=0.01, L1_reg = 0.00, \ |
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134 L2_reg = 0.0001, n_iter=100,n_hidden=[200,100,90,80,70]): |
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135 """ |
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136 Demonstrate stochastic gradient descent optimization for a multilayer |
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137 perceptron |
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138 |
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139 This is demonstrated on MNIST. |
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140 |
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141 :param learning_rate: learning rate used (factor for the stochastic |
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142 gradient |
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143 |
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144 :param L1_reg: L1-norm's weight when added to the cost (see |
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145 regularization) |
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146 |
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147 :param L2_reg: L2-norm's weight when added to the cost (see |
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148 regularization) |
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149 |
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150 :param n_iter: maximal number of iterations ot run the optimizer |
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151 |
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152 """ |
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153 |
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154 # Load the dataset |
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155 f = gzip.open('mnist.pkl.gz','rb') |
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156 train_set, valid_set, test_set = cPickle.load(f) |
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157 f.close() |
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158 |
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159 # make minibatches of size 20 |
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160 batch_size = 20 # sized of the minibatch |
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161 |
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162 # Dealing with the training set |
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163 # get the list of training images (x) and their labels (y) |
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164 (train_set_x, train_set_y) = train_set |
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165 |
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166 # initialize the list of training minibatches with empty list |
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167 train_batches = [] |
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168 for i in xrange(0, len(train_set_x), batch_size): |
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169 # add to the list of minibatches the minibatch starting at |
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170 # position i, ending at position i+batch_size |
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171 # a minibatch is a pair ; the first element of the pair is a list |
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172 # of datapoints, the second element is the list of corresponding |
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173 # labels |
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174 train_batches = train_batches + \ |
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175 [(train_set_x[i:i+batch_size], train_set_y[i:i+batch_size])] |
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176 |
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177 # Dealing with the validation set |
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178 (valid_set_x, valid_set_y) = valid_set |
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179 # initialize the list of validation minibatches |
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180 valid_batches = [] |
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181 for i in xrange(0, len(valid_set_x), batch_size): |
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182 valid_batches = valid_batches + \ |
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183 [(valid_set_x[i:i+batch_size], valid_set_y[i:i+batch_size])] |
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184 |
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185 # Dealing with the testing set |
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186 (test_set_x, test_set_y) = test_set |
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187 # initialize the list of testing minibatches |
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188 test_batches = [] |
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189 for i in xrange(0, len(test_set_x), batch_size): |
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190 test_batches = test_batches + \ |
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191 [(test_set_x[i:i+batch_size], test_set_y[i:i+batch_size])] |
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192 |
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193 |
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194 ishape = (28,28) # this is the size of MNIST images |
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195 |
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196 # allocate symbolic variables for the data |
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197 x = T.fmatrix() # the data is presented as rasterized images |
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198 y = T.lvector() # the labels are presented as 1D vector of |
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199 # [long int] labels |
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200 |
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201 # construct the logistic regression class |
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202 classifier = MLP( input=x.reshape((batch_size,28*28)),\ |
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203 n_in=28*28, n_hidden=n_hidden, n_out=10) |
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204 |
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205 # the cost we minimize during training is the negative log likelihood of |
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206 # the model plus the regularization terms (L1 and L2); cost is expressed |
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207 # here symbolically |
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208 cost = classifier.negative_log_likelihood(y) \ |
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209 + L1_reg * classifier.L1 \ |
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210 + L2_reg * classifier.L2_sqr |
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211 |
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212 # compiling a theano function that computes the mistakes that are made by |
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213 # the model on a minibatch |
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214 test_model = theano.function([x,y], classifier.errors(y)) |
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215 g_W=[] |
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216 g_b=[] |
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217 # compute the gradient of cost with respect to theta = (W1, b1, W2, b2) |
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218 for i in range(len(n_hidden)+1): |
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219 g_W.append(T.grad(cost, classifier.W[i])) |
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220 g_b.append(T.grad(cost, classifier.b[i])) |
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221 |
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222 |
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223 # specify how to update the parameters of the model as a dictionary |
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224 updates={} |
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225 for i in range(len(n_hidden)+1): |
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226 updates[classifier.W[i]]= classifier.W[i] - learning_rate*g_W[i] |
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227 updates[classifier.b[i]]= classifier.b[i] - learning_rate*g_b[i] |
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228 # compiling a theano function `train_model` that returns the cost, but in |
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229 # the same time updates the parameter of the model based on the rules |
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230 # defined in `updates` |
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231 train_model = theano.function([x, y], cost, updates = updates ) |
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232 n_minibatches = len(train_batches) |
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233 |
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234 # early-stopping parameters |
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235 patience = 10000 # look as this many examples regardless |
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236 patience_increase = 2 # wait this much longer when a new best is |
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237 # found |
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238 improvement_threshold = 0.995 # a relative improvement of this much is |
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239 # considered significant |
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240 validation_frequency = n_minibatches # go through this many |
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241 # minibatche before checking the network |
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242 # on the validation set; in this case we |
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243 # check every epoch |
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244 |
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245 |
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246 best_params = None |
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247 best_validation_loss = float('inf') |
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248 best_iter = 0 |
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249 test_score = 0. |
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250 start_time = time.clock() |
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251 # have a maximum of `n_iter` iterations through the entire dataset |
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252 for iter in xrange(n_iter* n_minibatches): |
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253 |
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254 # get epoch and minibatch index |
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255 epoch = iter / n_minibatches |
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256 minibatch_index = iter % n_minibatches |
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257 |
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258 # get the minibatches corresponding to `iter` modulo |
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259 # `len(train_batches)` |
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260 x,y = train_batches[ minibatch_index ] |
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261 cost_ij = train_model(x,y) |
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262 |
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263 if (iter+1) % validation_frequency == 0: |
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264 # compute zero-one loss on validation set |
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265 this_validation_loss = 0. |
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266 for x,y in valid_batches: |
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267 # sum up the errors for each minibatch |
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268 this_validation_loss += test_model(x,y) |
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269 # get the average by dividing with the number of minibatches |
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270 this_validation_loss /= len(valid_batches) |
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271 |
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272 print('epoch %i, minibatch %i/%i, validation error %f %%' % \ |
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273 (epoch, minibatch_index+1, n_minibatches, \ |
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274 this_validation_loss*100.)) |
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275 |
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276 |
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277 # if we got the best validation score until now |
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278 if this_validation_loss < best_validation_loss: |
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279 |
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280 #improve patience if loss improvement is good enough |
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281 if this_validation_loss < best_validation_loss * \ |
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282 improvement_threshold : |
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283 patience = max(patience, iter * patience_increase) |
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284 |
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285 # save best validation score and iteration number |
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286 best_validation_loss = this_validation_loss |
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287 best_iter = iter |
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288 |
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289 # test it on the test set |
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290 test_score = 0. |
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291 for x,y in test_batches: |
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292 test_score += test_model(x,y) |
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293 test_score /= len(test_batches) |
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294 print((' epoch %i, minibatch %i/%i, test error of best ' |
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295 'model %f %%') % |
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296 (epoch, minibatch_index+1, n_minibatches, |
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297 test_score*100.)) |
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298 |
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299 if patience <= iter : |
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300 break |
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301 |
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302 end_time = time.clock() |
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303 print(('Optimization complete. Best validation score of %f %% ' |
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304 'obtained at iteration %i, with test performance %f %%') % |
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305 (best_validation_loss * 100., best_iter, test_score*100.)) |
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306 print ('The code ran for %f minutes' % ((end_time-start_time)/60.)) |
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307 #test on NIST (you need pylearn and access to NIST to do that) |
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308 if __name__ == '__main__': |
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309 sgd_optimization_mnist() |
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310 |