Fittable Exponential function with handles:
y(x) = A exp(-(x-x0)/E)
A = amplitude, corresponding to function value for x=x0
x0 = origin, corresponding to y(xo) = A
E = reciprocal exponent (decay constant)
The initial function will be a negative exponential based
on the current maximum and minimum axis values (not the data).
Fittable Lorentzian function with handles:
y(x) = A*(g/2)^2/((x-x0)^2+(g/2)^2)
A = maximum value of the function
x0 = origin, corresponding to the maximum value of y(x)
g = width
Also known as a Breit-Wigner distribution in nuclear physics.