FWHM version of Gaussian Function.
Number: 4
Names: y0, xc, A, w
Meanings: y0 = base, xc = center, A = area, w = FWHM
Lower Bounds: w > 0.0
Upper Bounds: none
nlf_Gaussian(x,y0,xc,A,w)
FITFUNC\Gaussian.fdf
Peak Functions, PFW