Figure 2: Plots of the derivatives of erfc. The points are the 0- and 1st-order derivatives at and . Also shown for comparison is the derivative from Coimbra's operator (2.15) (dashed line). (a) Riemann-Liouville type operator (2.13) with (thin line), (medium line), (thick line). (b) Caputo-type definition (2.14) with (thin line), (medium line), (thick line). In this case the operator (2.14) with exponent does not match Coimbra's operator, but is equivalent to the first derivative at (c) Definition (2.11) (thin line).