title: tensorflow InvalidArgumentError: You must feed a value for placeholder tensor with dtype float
body: <p>I am new to tensorflow and want to train a logistic model for classification.</p>
  
  <pre><code># Set model weights
  W = tf.Variable(tf.zeros([30, 16]))
  b = tf.Variable(tf.zeros([16]))
  train_X, train_Y, X, Y = input('train.csv')
  
  #construct model
  pred = model(X, W, b)
  # Minimize error using cross entropy
  cost = tf.reduce_mean(-tf.reduce_sum(Y*tf.log(pred), reduction_indices=1))
  # Gradient Descent
  learning_rate = 0.1
  #optimizer = tf.train.AdamOptimizer(learning_rate).minimize(cost)
  optimizer = tf.train.GradientDescentOptimizer(learning_rate).minimize(cost)
  # Initializing the variables
  init = tf.initialize_all_variables()
  
  get_ipython().magic(u'matplotlib inline')
  import collections
  import matplotlib.pyplot as plt
  
  training_epochs = 200
  batch_size = 300
  train_X, train_Y, X, Y = input('train.csv')
  acc = []
  x = tf.placeholder(tf.float32, [None, 30]) 
  y = tf.placeholder(tf.float32, [None, 16])
  with tf.Session() as sess:
       sess.run(init)
       # Training cycle
       for epoch in range(training_epochs):
           avg_cost = 0.0
           #print(type(y_train[0][0]))
           print(type(train_X))
           print(type(train_X[0][0]))
           print X
           _, c = sess.run([optimizer, cost], feed_dict = {x: train_X, y: train_Y})
  </code></pre>
  
  <p>The feef_dict method does not work, with the complain: </p>
  
  <blockquote>
    <p>InvalidArgumentError: You must feed a value for placeholder tensor
    'Placeholder_54' with dtype float      [[Node: Placeholder_54 =
    Placeholderdtype=DT_FLOAT, shape=[],
    _device="/job:localhost/replica:0/task:0/cpu:0"]] Caused by op u'Placeholder_54':</p>
  </blockquote>
  
  <p>I check the data type, for the training feature data X:</p>
  
  <pre><code>  train_X type: &lt;type 'numpy.ndarray'&gt;
    train_X[0][0]: &lt;type 'numpy.float32'&gt;
    train_X size: (300, 30)
    place_holder info : Tensor("Placeholder_56:0", shape=(?, 30), dtype=float32)
  </code></pre>
  
  <p>I do not know why it complains. Hope sb could help, thanks</p>