Perceptron in Mathematical Notation

$$\begin{array}{ll}{x}_1,x_2,x_3& \text{ input vector components, features,... }\\ \mathbf{x}& \text{ example, input data, input... }\\ \text{w}& \text{ weight vector }\\ \sigma & \text{ activation function }\\ \text{ read the graphics above as: }y=\sigma \left({\sum }_{i=1}^3{w}_i{x}_i\right)& \end{array}$$