Ramp function

The ramp function, $R(x)$ is given by

Failed to parse (Conversion error. Server ("https://wikimedia.org/api/rest_") reported: "Cannot get mml. Server problem."): {\displaystyle R(x)\equiv xH(x)}

or

Failed to parse (Conversion error. Server ("https://wikimedia.org/api/rest_") reported: "Cannot get mml. Server problem."): {\displaystyle R(x)\equiv H(x)*H(x)}

with

Failed to parse (Conversion error. Server ("https://wikimedia.org/api/rest_") reported: "Cannot get mml. Server problem."): {\displaystyle {\frac {{\rm {d}}R(x)}{{\rm {d}}x}}=H(x)}

where is the Heaviside step distribution.