iFit/pseudovoigt

 y = pseudovoigt(p, x, [y]) : Pseudo Voigt

   iFunc/pseudovoigt Pseudo Voigt fitting function
     approximation of the convolution of gauss and lorz
         y = a * (d * (1/(1+((x-b)/c)^2)) + (1-d) * exp(-0.5 * ((x-b)/c)^2))

 pseudovoigt(width)          creates a model with a specified width
 pseudovoigt([ parameters ]) creates a model with specified model parameters

 Reference: http://en.wikipedia.org/wiki/Voigt_profile
            P. Thompson, D.E. Cox, J.B. Hastings, J. Appl. Cryst. 1987, 20, 79.

 input:  p: Pseudo Voigt model parameters (double)
            p = [ Amplitude Centre HalfWidth BackGround LorentzianRatio ]
          or 'guess'
         x: axis (double)
         y: when values are given and p='guess', a guess of the parameters is performed (double)
 output: y: model value
 ex:     y=pseudovoigt([1 0 1 1], -10:10); or plot(pseudovoigt);

 Version: Aug. 22, 2017
 See also iFunc, iFunc/fits, iFunc/plot
 (c) E.Farhi, ILL. License: EUPL.