title: Adding more layers to tensorflow MNIST tutorial makes accuracy drop
body: <p>Novice to deep learning. 
  With MNIST_SOFTMAX.py tutorial from gogoel tensorflow (   <a href="https://github.com/tensorflow/tensorflow/blob/master/tensorflow/examples/tutorials/mnist/mnist_softmax.py" rel="nofollow noreferrer">https://github.com/tensorflow/tensorflow/blob/master/tensorflow/examples/tutorials/mnist/mnist_softmax.py</a>), I added two new layers just to see what happen. </p>
  
  <pre><code>x = tf.placeholder(tf.float32, [None, 784])
  W = tf.Variable(tf.zeros([784, 10]))
  b = tf.Variable(tf.zeros([10]))
  y = tf.matmul(x, W) + b
  </code></pre>
  
  <p>Changed code above into </p>
  
  <pre><code>x = tf.placeholder(tf.float32, [None, 784])
  W1 = tf.Variable(tf.zeros([784, 256]))
  W2 = tf.Variable(tf.zeros([256, 256]))
  W3 = tf.Variable(tf.zeros([256, 10]))
  
  B1 = tf.Variable(tf.zeros([256]))
  B2 = tf.Variable(tf.zeros([256]))
  B3 = tf.Variable(tf.zeros([10]))
  
  Y1 = tf.matmul(x, W1) + B1
  Y2 = tf.matmul(Y1, W2) + B2
  Y3 = tf.matmul(Y2, W3) + B3
  y = Y3
  </code></pre>
  
  <p>it drops accuracy from 0.9188 to 0.1028. can I get some idea of why it drops.</p>