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Backpropagation

## Overview#

Backpropagation is a method used in Artificial Neural networks to calculate Loss function which tells you how you need to change a single Training dataset entry in terms of the relative proportions of the weight and bias for the Artificial Neuron so as to most efficiently decrease the loss.

Backpropagation involves the averaging the Loss function for every entry within the Training dataset for each Artificial Neuron in each layer to determine the total Cost function

Backpropagation is a method used in Artificial Neural networks to calculate the error contribution of each neuron after a batch of data (in image recognition, multiple images) is processed.

Backpropagation is a special case of an older and more general technique called automatic differentiation. In the context of learning, Backpropagation is commonly used by the gradient descent optimization algorithm to adjust the weight of neurons by calculating the gradient of the loss function. This technique is also sometimes called Backpropagation of errors, because the error is calculated at the output and distributed back through the network layers.

Backpropagation algorithm has been repeatedly rediscovered and is equivalent to automatic differentiation in reverse accumulation mode.

Backpropagation requires a known, desired output for each input value—it is therefore considered to be a Supervised Learning method (although it is used in some unsupervised networks such as autoencoders).

Backpropagation is also a generalization of the delta rule to multi-layered Feedforward Neural networks, made possible by using the chain rule to iteratively compute gradients for each layer. Backpropagation is closely related to the Gauss–Newton algorithm, and is part of continuing research in neural Backpropagation.

Backpropagation can be used with any gradient-based optimizer, such as L-BFGS or truncated Newton.

Backpropagation is commonly used to train Deep Learning Artificial Neural networks with more than one hidden node.

### Backpropagation to find Gradient descent in Python#

```dw = 1/m*np.dot(X,(A-Y).T)
db = 1/m*np.sum(A-Y)
```

Backpropagation is an Algorithm for the partial derivative ∂C/∂w of the Cost function "C" with respect to any weight w (or bias b) in the network. The expression tells us how quickly the cost changes when we change the weights and biases. And while the expression is somewhat complex, it also has a beauty to it, with each element having a natural, intuitive interpretation. And so backpropagation isn't just a fast algorithm for learning. It actually gives us detailed insights into how changing the weights and biases changes the overall behaviour of the Artificial Neural network.

### Category#

Artificial Intelligence

• [#1] - Backpropagation - based on information obtained 2017-11-24-