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import os
import numpy as np
import tensorflow as tf
from tensorflow.examples.tutorials.mnist import input_data
import time



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# Define paramaters for the model
learning_rate = 0.01
batch_size = 128
n_epochs = 10

Step 1: Read in data
using TF Learn's built in function to load MNIST data to the folder data/mnist



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mnist = input_data.read_data_sets('/data/mnist', one_hot=True)

Step 2: create placeholders for features and labels
each image in the MNIST data is of shape 28*28 = 784
therefore, each image is represented with a 1x784 tensor
there are 10 classes for each image, corresponding to digits 0 - 9.
Features are of the type float, and labels are of the type int



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Step 3: create weights and bias
weights and biases are initialized to 0
shape of w depends on the dimension of X and Y so that Y = X * w + b
shape of b depends on Y



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Step 4: build model
the model that returns the logits.
this logits will be later passed through softmax layer
to get the probability distribution of possible label of the image
DO NOT DO SOFTMAX HERE



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Step 5: define loss function
use cross entropy loss of the real labels with the softmax of logits
use the method:
tf.nn.softmax_cross_entropy_with_logits(logits, Y)
then use tf.reduce_mean to get the mean loss of the batch



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Step 6: define training op
using gradient descent to minimize loss



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with tf.Session() as sess:
	start_time = time.time()
	sess.run(tf.global_variables_initializer())	
	n_batches = int(mnist.train.num_examples/batch_size)
	for i in range(n_epochs): # train the model n_epochs times
		total_loss = 0

		for _ in range(n_batches):
			X_batch, Y_batch = mnist.train.next_batch(batch_size)
			# TO-DO: run optimizer + fetch loss_batch
			# 
			# 
			total_loss += loss_batch
		print('Average loss epoch {0}: {1}'.format(i, total_loss/n_batches))

	print('Total time: {0} seconds'.format(time.time() - start_time))

	print('Optimization Finished!') # should be around 0.35 after 25 epochs

	# test the model
	preds = tf.nn.softmax(logits)
	correct_preds = tf.equal(tf.argmax(preds, 1), tf.argmax(Y, 1))
	accuracy = tf.reduce_sum(tf.cast(correct_preds, tf.float32)) # need numpy.count_nonzero(boolarr) :(
	
	n_batches = int(mnist.test.num_examples/batch_size)
	total_correct_preds = 0
	
	for i in range(n_batches):
		X_batch, Y_batch = mnist.test.next_batch(batch_size)
		accuracy_batch = sess.run([accuracy], feed_dict={X: X_batch, Y:Y_batch}) 
		total_correct_preds += accuracy_batch	
	
	print('Accuracy {0}'.format(total_correct_preds/mnist.test.num_examples))