Yesterday, I was considering going for The Most Epic Action Movie Ever. Since it was an action movie, I was up right away. A quick search online revealed it having good ratings. That’s great! I called my friends, informed my plans and they jumped in. All boxes ticked, so I went.
The decision process can be visualized as below.

Here is how I made the decision:
It’s an action movie (+1 point) with a good rating (+1 point) and my friends are coming (+1 point). Total = +3
Now, my decision parameter is if I get a total of 3 points then I will go, else I won’t.

(1) going if points = 3
(0) not going if points < 3

It is possible that I am ok with meeting just two of the criteria. In which case:

(1) going if points >= 2
(0) not going if points < 2 

This decision parameter is called an activation function. I am going to represent activation function as the following from now on.

If I am limited by budget then,

Here, I have introduced a penalty. Suppose the movie tickets do not fit my budget but all else holds true. I will calculate my points as:

Since 1 < 2 I will not be going for the movie.
These numbers on the edges between the nodes are called weights. So far I have covered weights and inputs. Let’s try to write this in a generalized form.

Let x1 denote rating input, x2 be action input and so on.
Let w1 denote the weight between rating and output node. w2 between action and output and so on.
The equation then becomes:

$$x_1 w_1 + x_2 w_2 + x_3 w_3 + x_4 w_4$$

This can be written as $$\sum_{i=1} ^4 x_i w_i$$

Let f(x) be the activation function. Then the whole equation can be represented as:

$$f(\sum_{i=1} ^4 x_i w_i)$$

However, there is another term remaining called bias.
Bias is essentailly another input which is always on (set to 1). It is used to shift the activation threshold.

This can be interpreted as, if I am a movie buff I will go in any case. If however, I don’t like movies, I won’t go at all. Now, these are the examples of two extreme cases but the idea that bias shifts the threshold of activation is clearly illustrated.
The general function now becomes:

$$f(\sum_{i=1} ^4 x_i w_i + b)$$

This is the general architecture of an artificial neuron. There are many different architectures of artificial neural networks such as RNNs, Feed-forward and Convolutional NN. Even different varieties of activation functions haven’t been explored. And, concepts such as back-propagation, momentum and dropouts haven’t been touched. In the following posts, I am going to cover all these concepts.

Hey! You have reached the end 😎. Thanks for reading.