lab 03.X minimizing cost tf gradient

# Lab 3 Minimizing Cost
# This is optional
import tensorflow as tf
tf.set_random_seed(777)  # for reproducibility

# tf Graph Input
X = [1, 2, 3]
Y = [1, 2, 3]

# Set wrong model weights
W = tf.Variable(5.)

# Linear model
hypothesis = X * W

# Manual gradient
gradient = tf.reduce_mean((W * X - Y) * X) * 2

# cost/loss function
cost = tf.reduce_mean(tf.square(hypothesis - Y))

# Minimize: Gradient Descent Magic
optimizer = tf.train.GradientDescentOptimizer(learning_rate=0.01)
train = optimizer.minimize(cost)

# Get gradients
gvs = optimizer.compute_gradients(cost, [W])
# Optional: modify gradient if necessary
# gvs = [(tf.clip_by_value(grad, -1., 1.), var) for grad, var in gvs]
# Apply gradients
apply_gradients = optimizer.apply_gradients(gvs)

# Launch the graph in a session.
sess = tf.Session()
# Initializes global variables in the graph.
sess.run(tf.global_variables_initializer())

for step in range(100):
    print(step, sess.run([gradient, W, gvs]))
    sess.run(apply_gradients)
    # Same as sess.run(train)


'''
# Apply gradients
0 [37.333332, 5.0, [(37.333336, 5.0)]]
1 [33.848888, 4.6266665, [(33.848888, 4.6266665)]]
2 [30.689657, 4.2881775, [(30.689657, 4.2881775)]]
3 [27.825287, 3.9812808, [(27.825287, 3.9812808)]]
4 [25.228262, 3.703028, [(25.228264, 3.703028)]]
...
96 [0.0030694802, 1.0003289, [(0.0030694804, 1.0003289)]]
97 [0.0027837753, 1.0002983, [(0.0027837753, 1.0002983)]]
98 [0.0025234222, 1.0002704, [(0.0025234222, 1.0002704)]]
99 [0.0022875469, 1.0002451, [(0.0022875469, 1.0002451)]]
'''