The graph in the question does not represent a linear function because a linear function is always a straight line, and is represented by the following equation:
y = f(x) = a + bx
The function illustrated in the graph looks more like a logarithmic function that is flattening as it progresses.
Explanation: Tone is achieved through word choice (diction), sentence construction and word order (syntax), and by what the viewpoint character focuses on.
