Such functions are called linear, for reasons that I'll explain soon enough (well, we generally want another condition for linear functions involving scalar multiples of the variable, but I'll ...

Bo HU, Jun SHAO, Mari PALTA, Variability explained by covariates in linear mixed-effect models for longitudinal data, The Canadian Journal of Statistics / La Revue Canadienne de Statistique, Vol. 38, ...

Many data are suitably modeled by functions consisting of straight-line segments. These functions may be called piecewise-linear. Smooth functions that are related to the hyperbola and that have ...