The BBTT_Order algorithm performs an update on a recurrent network. The recurrent net can be transformed into a regular feedforward net with an input, multiple hidden and output layer. At the beginning the update procedure checks if there is a zero-input pattern in the input layer. Suppose there is such a pattern, then the so called i_act value buffer is set to 0 for all neurons. In this case i_act can be seen as a buffer for the output value of the hidden and output neurons. The next step is to copy the i_act value to the output of all hidden and output neurons. The new activation of the hidden and output units will be calculated. Now the new output for every neuron in the hidden and output layer will be computed and stored in i_act.