part2_neural_network_mnist_data.ipynb

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  {
   "cell_type": "code",
   "execution_count": 1,
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   "source": [
    "# python notebook for Make Your Own Neural Network\n",
    "# code for a 3-layer neural network, and code for learning the MNIST dataset\n",
    "# (c) Tariq Rashid, 2016\n",
    "# license is GPLv2"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "import numpy\n",
    "# scipy.special for the sigmoid function expit()\n",
    "import scipy.special\n",
    "# library for plotting arrays\n",
    "import matplotlib.pyplot\n",
    "# ensure the plots are inside this notebook, not an external window\n",
    "%matplotlib inline"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [],
   "source": [
    "# neural network class definition\n",
    "class neuralNetwork:\n",
    "    \n",
    "    \n",
    "    # initialise the neural network\n",
    "    def __init__(self, inputnodes, hiddennodes, outputnodes, learningrate):\n",
    "        # set number of nodes in each input, hidden, output layer\n",
    "        self.inodes = inputnodes\n",
    "        self.hnodes = hiddennodes\n",
    "        self.onodes = outputnodes\n",
    "        \n",
    "        # link weight matrices, wih and who\n",
    "        # weights inside the arrays are w_i_j, where link is from node i to node j in the next layer\n",
    "        # w11 w21\n",
    "        # w12 w22 etc \n",
    "        self.wih = numpy.random.normal(0.0, pow(self.inodes, -0.5), (self.hnodes, self.inodes))\n",
    "        self.who = numpy.random.normal(0.0, pow(self.hnodes, -0.5), (self.onodes, self.hnodes))\n",
    "\n",
    "        # learning rate\n",
    "        self.lr = learningrate\n",
    "        \n",
    "        # activation function is the sigmoid function\n",
    "        self.activation_function = lambda x: scipy.special.expit(x)\n",
    "        \n",
    "        pass\n",
    "\n",
    "    \n",
    "    # train the neural network\n",
    "    def train(self, inputs_list, targets_list):\n",
    "        # convert inputs list to 2d array\n",
    "        inputs = numpy.array(inputs_list, ndmin=2).T\n",
    "        targets = numpy.array(targets_list, ndmin=2).T\n",
    "        \n",
    "        # calculate signals into hidden layer\n",
    "        hidden_inputs = numpy.dot(self.wih, inputs)\n",
    "        # calculate the signals emerging from hidden layer\n",
    "        hidden_outputs = self.activation_function(hidden_inputs)\n",
    "        \n",
    "        # calculate signals into final output layer\n",
    "        final_inputs = numpy.dot(self.who, hidden_outputs)\n",
    "        # calculate the signals emerging from final output layer\n",
    "        final_outputs = self.activation_function(final_inputs)\n",
    "        \n",
    "        # output layer error is the (target - actual)\n",
    "        output_errors = targets - final_outputs\n",
    "        # hidden layer error is the output_errors, split by weights, recombined at hidden nodes\n",
    "        hidden_errors = numpy.dot(self.who.T, output_errors) \n",
    "        \n",
    "        # update the weights for the links between the hidden and output layers\n",
    "        self.who += self.lr * numpy.dot((output_errors * final_outputs * (1.0 - final_outputs)), numpy.transpose(hidden_outputs))\n",
    "        \n",
    "        # update the weights for the links between the input and hidden layers\n",
    "        self.wih += self.lr * numpy.dot((hidden_errors * hidden_outputs * (1.0 - hidden_outputs)), numpy.transpose(inputs))\n",
    "        \n",
    "        pass\n",
    "\n",
    "    \n",
    "    # query the neural network\n",
    "    def query(self, inputs_list):\n",
    "        # convert inputs list to 2d array\n",
    "        inputs = numpy.array(inputs_list, ndmin=2).T\n",
    "        \n",
    "        # calculate signals into hidden layer\n",
    "        hidden_inputs = numpy.dot(self.wih, inputs)\n",
    "        # calculate the signals emerging from hidden layer\n",
    "        hidden_outputs = self.activation_function(hidden_inputs)\n",
    "        \n",
    "        # calculate signals into final output layer\n",
    "        final_inputs = numpy.dot(self.who, hidden_outputs)\n",
    "        # calculate the signals emerging from final output layer\n",
    "        final_outputs = self.activation_function(final_inputs)\n",
    "        \n",
    "        return final_outputs"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [],
   "source": [
    "# number of input, hidden and output nodes\n",
    "input_nodes = 784\n",
    "hidden_nodes = 200\n",
    "output_nodes = 10\n",
    "\n",
    "# learning rate\n",
    "learning_rate = 0.1\n",
    "\n",
    "# create instance of neural network\n",
    "n = neuralNetwork(input_nodes,hidden_nodes,output_nodes, learning_rate)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [],
   "source": [
    "# load the mnist training data CSV file into a list\n",
    "training_data_file = open(\"mnist_dataset/mnist_train.csv\", 'r')\n",
    "training_data_list = training_data_file.readlines()\n",
    "training_data_file.close()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [],
   "source": [
    "# train the neural network\n",
    "\n",
    "# epochs is the number of times the training data set is used for training\n",
    "epochs = 5\n",
    "\n",
    "for e in range(epochs):\n",
    "    # go through all records in the training data set\n",
    "    for record in training_data_list:\n",
    "        # split the record by the ',' commas\n",
    "        all_values = record.split(',')\n",
    "        # scale and shift the inputs\n",
    "        inputs = (numpy.asfarray(all_values[1:]) / 255.0 * 0.99) + 0.01\n",
    "        # create the target output values (all 0.01, except the desired label which is 0.99)\n",
    "        targets = numpy.zeros(output_nodes) + 0.01\n",
    "        # all_values[0] is the target label for this record\n",
    "        targets[int(all_values[0])] = 0.99\n",
    "        n.train(inputs, targets)\n",
    "        pass\n",
    "    pass"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# load the mnist test data CSV file into a list\n",
    "test_data_file = open(\"mnist_dataset/mnist_test.csv\", 'r')\n",
    "test_data_list = test_data_file.readlines()\n",
    "test_data_file.close()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [],
   "source": [
    "# test the neural network\n",
    "\n",
    "# scorecard for how well the network performs, initially empty\n",
    "scorecard = []\n",
    "\n",
    "# go through all the records in the test data set\n",
    "for record in test_data_list:\n",
    "    # split the record by the ',' commas\n",
    "    all_values = record.split(',')\n",
    "    # correct answer is first value\n",
    "    correct_label = int(all_values[0])\n",
    "    # scale and shift the inputs\n",
    "    inputs = (numpy.asfarray(all_values[1:]) / 255.0 * 0.99) + 0.01\n",
    "    # query the network\n",
    "    outputs = n.query(inputs)\n",
    "    # the index of the highest value corresponds to the label\n",
    "    label = numpy.argmax(outputs)\n",
    "    # append correct or incorrect to list\n",
    "    if (label == correct_label):\n",
    "        # network's answer matches correct answer, add 1 to scorecard\n",
    "        scorecard.append(1)\n",
    "    else:\n",
    "        # network's answer doesn't match correct answer, add 0 to scorecard\n",
    "        scorecard.append(0)\n",
    "        pass\n",
    "    \n",
    "    pass"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "performance =  0.9712\n"
     ]
    }
   ],
   "source": [
    "# calculate the performance score, the fraction of correct answers\n",
    "scorecard_array = numpy.asarray(scorecard)\n",
    "print (\"performance = \", scorecard_array.sum() / scorecard_array.size)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
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   "source": []
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