%%%--------------------------MODEL DESCRIPTION--------------------------%%%
Model to fit pair correlation data to a gamma distribution

|Amplitude|/|x|*|exp(- |(lnx-�)^2/ |(2sigma^2)|)
%%%-------------------------PARAMETER DEFINITION------------------------%%%
Param(1): A             = 1;    LB = 0;     UB = Inf;
Param(2): alpha         = 1;   LB = 1;     UB = Inf;   
Param(3): beta          = 1;    LB = 0;     UB = Inf;
Param(4): y0            = 0;    LB = -10;   UB = 10;
%%%------------------------BRIGHTNESS DEFINITION------------------------%%%
B=1/P(1); 
%%%-----------------------------FIT FUNCTION----------------------------%%%  
OUT=P(1)*P(3)^P(2)*x.^(P(2)-1).*exp(-x*P(3))/gamma(P(2));