# What is the difference between backpropagation and Backpropagation Through Time?

## What is the difference between backpropagation and Backpropagation Through Time?

The Backpropagation algorithm is suitable for the feed forward neural network on fixed sized input-output pairs. The Backpropagation Through Time is the application of Backpropagation training algorithm which is applied to the sequence data like the time series.

## Is back propagation possible in RNN?

You see, a RNN essentially processes sequences one step at a time, so during backpropagation the gradients flow backward across time steps. This is called backpropagation through time. So, the gradient wrt the hidden state and the gradient from the previous time step meet at the copy node where they are summed up.

**What is the time complexity of backpropagation algorithm?**

Back-propagation algorithm For l→k, we thus have the time complexity O(lt+lt+ltk+lk)=O(l∗t∗k).

**Does real time recurrent learning is faster than BPTT?**

BPTT tends to be significantly faster for training recurrent neural networks than general-purpose optimization techniques such as evolutionary optimization.

### What is the difference between BPTT and RTRL algorithms?

A more computationally expensive online variant is called “Real-Time Recurrent Learning” or RTRL, which is an instance of automatic differentiation in the forward accumulation mode with stacked tangent vectors. Unlike BPTT, this algorithm is local in time but not local in space.

### What is RNN architecture?

A recurrent neural network (RNN) is a special kind of artificial neural network that permits continuing information related to past knowledge by utilizing a special kind of looped architecture. They are employed in many areas regarding data with sequences, such as predicting the next word of a sentence.

**Does LSTM use back propagation?**

LSTM (Long short term Memory ) is a type of RNN(Recurrent neural network), which is a famous deep learning algorithm that is well suited for making predictions and classification with a flavour of the time.

**What is the time complexity of backtracking?**

Usually in this approach you either take [one input] into consideration and make a recursive call and then you don’t consider it and make another call. This makes the “recursive call tree” look like a binary tree which would have 2^N problems to solve (2^N nodes in that binary tree). So, the time complexity is 2^N.

## What is time complexity analysis?

Time complexity is an abstract way to represent the running time of an algorithm in terms of the rate of growth only. It is an approximate estimation of how much time an algorithm will take for a large value of input size. We use different notations to represent the best, average, and worst-case time complexity.

## What is Backpropagation Through Time in RNN?

Backpropagation Through Time, or BPTT, is the application of the Backpropagation training algorithm to recurrent neural network applied to sequence data like a time series. A recurrent neural network is shown one input each timestep and predicts one output. Conceptually, BPTT works by unrolling all input timesteps.

**What is truncated Backpropagation Through Time?**

Truncated Backpropagation Through Time (truncated BPTT) is a widespread method for learning recurrent computational graphs. Truncated BPTT keeps the computational benefits of Backpropagation Through Time (BPTT) while relieving the need for a complete backtrack through the whole data sequence at every step.

**What is real time recurrent learning?**

Real Time Recurrent Learning (RTRL) eliminates the need for history storage and allows for online weight updates, but does so at the expense of computational costs that are quartic in the state size. This renders RTRL training intractable for all but the smallest networks, even ones that are made highly sparse.

### Why is LSTM better than RNN?

Long Short-Term Memory LSTM LSTM networks are a type of RNN that uses special units in addition to standard units. LSTM units include a ‘memory cell’ that can maintain information in memory for long periods of time. This memory cell lets them learn longer-term dependencies.

### What is difference between CNN and RNN?

A CNN has a different architecture from an RNN. CNNs are “feed-forward neural networks” that use filters and pooling layers, whereas RNNs feed results back into the network (more on this point below). In CNNs, the size of the input and the resulting output are fixed.

**What is the problem with RNN?**

However, RNNs suffer from the problem of vanishing gradients, which hampers learning of long data sequences. The gradients carry information used in the RNN parameter update and when the gradient becomes smaller and smaller, the parameter updates become insignificant which means no real learning is done.

**Is LSTM faster than CNN?**

Since CNNs run one order of magnitude faster than both types of LSTM, their use is preferable. All models are robust with respect to their hyperparameters and achieve their maximal predictive power early on in the cases, usually after only a few events, making them highly suitable for runtime predictions.

## Is backtracking dynamic programming?

Backtracking is similar to Dynamic Programming in that it solves a problem by efficiently performing an exhaustive search over the entire set of possible options. Backtracking is different in that it structures the search to be able to efficiently eliminate large sub-sets of solutions that are no longer possible.