The function f : [latex]\mathbb{R}[/latex] → [latex]\mathbb{R}[/latex] : x ↦ 2x + 1 is an affine function.
The function f : [latex]\mathbb{R}[/latex] → [latex]\mathbb{R}[/latex] : x ↦ 3x also is an affine function, although it is generally called a linear function or a direct variation function. In this case, parameter b has a value of zero.