When you need to process sequences – daily stock prices, sensor measurements, etc. – in a program, you need a recurrent neural network (RNN).
RNNs are a sort of Neural Network where the output from one step is transferred as input to the new step. In conventional neural systems, all the data sources and outputs are autonomous of one another. However, in cases like when it is required to anticipate the following expression of a sentence, the previous words are required, and consequently, there is a need to recollect the past words.
This is where RNN comes into the picture. It created a Hidden Layer to solve these issues. The fundamental and most significant element of RNN is Hidden state, which remembers some data about a sequence.
RNNs have been generating accurate results in some of the most common real-world applications: Because of their ability to handle text effectively, RNNs are generally used in Natural Language Processing (NLP) tasks.
- Speech recognition
- Machine translation
- Music composition
- Handwriting recognition
- Grammar learning
This is why RNNs have gained immense popularity in the deep learning space.
Now let’s see the need for recurrent neural networks in Python.
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What is the Need for RNNs in Python?
To answer this question, we first need to address the problems associated with a Convolution Neural Network (CNN), also called vanilla neural nets.
The major problem with CNNs is that they can only work for pre-defined sizes, i.e. if they accept fixed-size inputs, they also give out fixed-size outputs.
Whereas, with RNNs, this problem is easily taken care of. RNNs allow developers to work with variable-length sequences for both inputs as well as outputs.
Below is an illustration of what RNNs look like:
Source: Andrej Karpathy
Here, the red color denotes inputs, green RNNs, and blue outputs.
Let’s understand each in detail.
One-to-one: These are also called plain or vanilla neural networks. They work with fixed input size to fixed output size and are independent of previous inputs.
Example: Image classification.
One-to-many: While the information as input is of fixed size, the output is a sequence of data.
Example: Image captioning (image is input, and output is a set of words).
Many-to-one: Input is a sequence of information and output is of a fixed size.
Example: Sentiment analysis (input is a set of words and output tells whether the set of words reflects a positive or negative sentiment).
Many-to-many: Input is a sequence of information and output is a sequence of data.
Example: Machine translation (RNN reads a sentence in English and gives an output of the sentence in the desired language).
Sequence processing with variable lengths makes RNNs so useful. Here’s how:
- Machine Translation: The best example of this is Google Translate. It works on many-to-many RNNs. As you know, the original text is input to an RNN, which yields translated text.
- Sentiment Analysis: You know how Google segregates negative reviews from the positive ones? It is achieved by a many-to-one RNN. When the text is fed into the RNN, it gives the output, reflecting the class in which the input lies.
Now let’s see how RNNs work.
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How do RNNs Work?
It’s best to understand the working of a recurrent neural network in Python by looking at an example.
Let’s suppose that there is a deeper network containing one output layer, three hidden layers, and one input layer.
Just as it is with other neural networks, in this case, too, each hidden layer will come with its own set of weights and biases.
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For the sake of this example, let’s consider that the weights and biases for layer 1 are (w1, b1), layer 2 are (w2, b2), and layer 3 are (w3, b3). These three layers are independent of each other and do not remember the previous results.
Now, here’s what the RNN will do:
- It will convert the independent activations into dependent ones by making all the layers contain the same weights and biases. This will, in turn, reduce the complexity of increasing parameters and remembering each of previous results by giving the output as input to the next hidden layer.
- Thus, all three layers will be intertwined into a single recurrent layer to contain the same weights and biases.
- To calculate the current state, you can use the following formula:
-
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Where,
= current state
= previous state
= input state
- To apply the Activation function (tanh), use the following formula:
Where,
= weight at the recurrent neuron
= weight at input neuron
- To calculate output, use the following formula:
Where,
= output
= weight at the output layer
Here’s a step-by-step explanation of how an RNN can be trained.
- At one time, input is given to the network.
- Now, you need to calculate its current state using the current input set and the previous state.
- The current will become  for the next step of the time.
- You can go as many time steps as you want and combine the data from all the previous states.
- As soon as all time steps are completed, use the final current state to calculate the final output.
- Compare this output to the actual output, i.e. the target output and the error between the two.
- Propagate the error back to the network and update the weights to train the RNN.
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Conclusion
To conclude, I would first like to point out the advantages of a Recurring Neural Network in Python:
- An RNN can remember all the information it receives. This is the characteristic that is most used in series prediction as it can remember the previous inputs.
- In RNN, the same transition function with the same parameters can be used at every time step.
It’s critical to understand that the recurrent neural network in Python has no language understanding. It is adequately an advanced pattern recognition machine. In any case, unlike methods like Markov chains or frequency analysis, the RNN makes predictions dependent on the ordering of components in the sequence.
Basically, if you say that people are just extraordinary pattern recognition machines and, in this manner, the recurrent neural system is just acting like a human-machine.
The uses of RNNs go a long way past content generation to machine translation, image captioning, and authorship identification. Even though RNNs cannot possibly replace humans, it’s possible that with all the more training information and a bigger model, a neural system would have the option to integrate new, sensible patent abstracts.
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Is CNN faster than RNN?
If we look at the computation time of both CNN and RNN, CNN is found to be very fast (~ 5x) as compared to RNN. Let us try to understand this in a better way with an example.
If a restaurant review is: ‘The service has been incredibly slow, and I am pretty much disappointed with this restaurant. The food quality was also mediocre.’ Here, there is sequential data present in the statement, where you might be trying to find out whether the sentiments are good or bad. The CNN model will be able to make the computations faster over here as it would be looking at only certain phrases, such as 'incredibly slow,' 'mediocre,' and 'disappointed.' Here, RNN might just confuse you by looking at several other parameters. CNN is a simpler model, which makes it more efficient than RNN.
What are the applications of RNN?
RNNs are pretty powerful machine learning models that are being used in plenty of areas. The main aim of RNN is to process the sequential data that is made available to it. Availability of sequential data is found in various domains. Some of its applications in different domains include Machine translation, Speech recognition, Call centre analysis, Prediction problems, Text summarization, Video tagging, Face detection, Image recognition, OCR applications, and Music composition.
What are some key differences between RNN and CNN?
RNNs are useful for analyzing sequential and temporal data like videos or text. On the other hand, CNN is useful for solving problems that are related to spatial data like images. In RNN, the sizes of inputs and outputs may vary, while in CNN, there is a fixed size for input as well as the resulting output. Some use cases for RNNs are machine translation, speech analysis, sentiment analysis, and prediction problems, while CNNs are useful in medical analysis, classification, and facial recognition.
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