smedge: smeared edge

A smeared edge (Ebisawa PhD thesis, implemented by Frank Marshall).

$$M(E) = \begin{array}{ll} 1 & E < E_c\\ [.2cm] \exp\left[-f... ...ight] \left[1-\exp((E_c-E)/W)\right] & E \geq E_c \end{array}$$

where:

par1=$E_c$	the threshold energy (keV)
par2=f	the maximum absorption factor at threshold
par3=$\alpha$	index for photo-electric cross-section (normally -2.67)
par4=W	smearing width (keV)