code: public Map<String, INDArray> feedForward(INDArray input, boolean train) {
          if (numInputArrays != 1)
              throw new UnsupportedOperationException("Cannot feedForward with single input for graph network with "
                      + numInputArrays + " expected inputs");
          setInput(0, input);
          return feedForward(train);
      }
docs: Conduct forward pass using a single input array. Note that this method can only be used with ComputationGraphs
  with a single input array.
  
  @param input The input array
  @param train If true: do forward pass at training time
  @return A map of activations for each layer (not each GraphVertex). Keys = layer name, values = layer activations