Pearson VII peak function.
Number: 4
Names: xc, A, w, mu
Meanings: xc = center, A =area, w = width, mu = profile shape factor
Lower Bounds: A > 0.0, w > 0.0, mu > 0.0
Upper Bounds: none
nlf_pearson7(x,xc,A,w,mu)
FITFUNC\PEARSON7.FDF
Spectroscopy, PFW, Peak Functions