tf.matmul上发生tensorflow错误

Question

我在代码下面的13行y = tf.matmul(W, x_data) + b中有错误， 我无法理解原因

import tensorflow as tf
import numpy as np   

x_data = np.float32(np.random.rand(2, 100))    
y_data = np.dot([0.100, 0.200], x_data) + 0.300    

b = tf.Variable(tf.zeros([1]))

W = tf.Variable(tf.random_uniform([1, 2], -1.0, 1.0))
y = tf.matmul(W, x_data) + b    

loss = tf.reduce_mean(tf.square(y - y_data))    
optimizer = tf.train.GradientDescentOptimizer(0.5)

train = optimizer.minimize(loss)    
init = tf.initialize_all_variables()

sess = tf.Session()
sess.run(init)
#sess.run(x_data)
for step in xrange(0, 201):
    sess.run(train)
    if step % 20 == 0:
        print step, sess.run(W), sess.run(b)
    #print "xdata=", x_data 
    #print "ydata=",    y_data