Multi-layer Perceptron

Sung-ju Kim

Content

  1. Prepare pseudo data
  2. Make model & Design cost function & optimizer
  3. Train & Draw graph
import tensorflow as tf
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.colors as colors
import matplotlib.cm as cmx
%matplotlib inline
plt.style.use('ggplot')

def pseudo_function(x, x_i, n_data):
    n_wave = 5
    exp_max = 1
    exp_min = -1
    bias = 0.5
    a = 1.5
    
    radian_unit = (np.pi * n_wave) / n_data
    exp_unit = (exp_max - exp_min) / n_data 
    
    y = np.sin(x_i*radian_unit)* np.exp(exp_max-(exp_unit*x_i)) + bias + a*x
    
    return y

n_data = 100
x_range = (-1, 1)

X_train = np.linspace(-1, 1, n_data,dtype=np.float32)
Y_train = np.array([pseudo_function(x,x_i,n_data) for x_i, x in enumerate(list(X_train))], dtype=np.float32)
plt.cla()
plt.plot(X_train, Y_train, 'ro', alpha=0.4, color='black')

png

# reshape for model
X_train = np.reshape(X_train, newshape=[-1,1])
Y_train = np.reshape(Y_train, newshape=[-1,1])
print("X_train shape : {}\nY_train shape : {}".format(np.shape(X_train), np.shape(X_train)))

X_train shape : (100, 1)
Y_train shape : (100, 1)

2. Make model & Design cost function & optimizer

\[{ u }_{ j }={ \phi }_{ relu }(\sum _{ i=0 }^{ n }{ { w }_{ ij }{ x }_{ i } } )\quad { y }_{ l }={ \phi }_{ relu }(\sum _{ j=0 }^{ m }{ { w }_{ jl }{ u }_{ j } } )\] \[{ x }_{ i }\quad :\quad i-th\quad value\quad of\quad input\quad x\\ { w }_{ ij }\quad :\quad weight\quad between\quad { x }_{ i }\quad and\quad { u }_{ j }\\ { u }_{ j }\quad :\quad activation\quad of\quad first\quad layer\\ { w }_{ jl }\quad :\quad weight\quad between\quad { u }_{ i }\quad and\quad { y }_{ l }\\ { \phi }_{ relu }\quad :\quad relu\quad activation\quad function\quad\] 
with tf.variable_scope('variable'):
    X = tf.placeholder(dtype=tf.float32, 
                       shape=[None,1],
                       name="X")
    Y = tf.placeholder(dtype=tf.float32,
                       shape=[None,1],
                       name="Y")
    learning_rate = tf.placeholder(dtype=tf.float32, name='learning_rate')

#  almost same wiht tf.contrib.layers.flatten
def flatten(x, name=None):
    with tf.variable_scope('flatten'):
        dims = x.get_shape().as_list()
        if len(dims) == 4:
            flattened = tf.reshape(
                x,
                shape=[-1, dims[1] * dims[2] * dims[3]])
        elif len(dims) == 2 or len(dims) == 1:
            flattened = x
        else:
            raise ValueError('Expected n dimensions of 1, 2 or 4.  Found:',
                             len(dims))

        return flattened

#  almost same wiht tf.layers.dense
def linear(x, n_output, name=None, activation=None):
    if len(x.get_shape()) != 2:
        x = flatten(x)

    n_input = x.get_shape().as_list()[1]
    with tf.variable_scope(name or "fc"):
        W = tf.get_variable(
            name='W',
            shape=[n_input, n_output],
            dtype=tf.float32,
            initializer=tf.contrib.layers.xavier_initializer())

        b = tf.get_variable(
            name='b',
            shape=[n_output],
            dtype=tf.float32,
            initializer=tf.constant_initializer(0.0))

        h = tf.nn.bias_add(
            name='h',
            value=tf.matmul(x, W),
            bias=b)

        if activation:
            h = activation(h)

        return h, W

with tf.variable_scope('mlp_model'):
    # declaration of model
    
    h, _ = linear(X, 16, name="layer_1", activation=tf.nn.relu)
    h, _ = linear(h, 16, name="layer_2", activation=tf.nn.relu)
    Y_pred, _ = linear(h, 1, name="layer_3")
    
    # optimization
    cost = tf.reduce_mean(tf.squared_difference(Y_pred, Y))
    optimizer = tf.train.AdamOptimizer(learning_rate).minimize(cost)
    init = tf.global_variables_initializer()

3. Train & Draw graph

lr = 0.005
n_epoch = 6000

draw_interval = 300
plt.cla()
plt.plot(X_train, Y_train, 'ro', alpha=0.4, label="origin", color="black")

cmap = plt.get_cmap('coolwarm')
c_norm = colors.Normalize(vmin=0, vmax=n_epoch)
scalar_map = cmx.ScalarMappable(norm=c_norm, cmap=cmap)

sess = tf.Session() 
sess.run(init)
for epoch_i in range(n_epoch):
    _ = sess.run(optimizer, feed_dict={X:X_train, 
                                   Y:Y_train, 
                                   learning_rate:lr})
    if epoch_i % draw_interval == 0 :
        X_show = X_train.copy()
        Y_show = sess.run(Y_pred, 
                          feed_dict={X:X_show})
        
        plt.plot(X_show, Y_show, alpha=epoch_i/n_epoch, color=scalar_map.to_rgba(epoch_i))

png