title: Tensorflow: Using Adam optimizer
body: <p>I am experimenting with some simple models in tensorflow, including one that looks very similar to the first <a href="http://www.tensorflow.org/tutorials/mnist/beginners/index.md">MNIST for ML Beginners example</a>, but with a somewhat larger dimensionality. I am able to use the gradient descent optimizer with no problems, getting good enough convergence. When I try to use the ADAM optimizer, I get errors like this:</p>
  
  <pre><code>tensorflow.python.framework.errors.FailedPreconditionError: Attempting to use uninitialized value Variable_21/Adam
       [[Node: Adam_2/update_Variable_21/ApplyAdam = ApplyAdam[T=DT_FLOAT, use_locking=false, _device="/job:localhost/replica:0/task:0/cpu:0"](Variable_21, Variable_21/Adam, Variable_21/Adam_1, beta1_power_2, beta2_power_2, Adam_2/learning_rate, Adam_2/beta1, Adam_2/beta2, Adam_2/epsilon, gradients_11/add_10_grad/tuple/control_dependency_1)]]
  </code></pre>
  
  <p>where the specific variable that complains about being uninitialized changes depending on the run. What does this error mean? And what does it suggest is wrong? It seems to occur regardless of the learning rate I use.</p>