%   [ r, p] = Brute_PCF(data, q_range)
%
%   Generate a Pair Correlation Function by Brute Force
%       Inputs -
%                   I versus q -->   data(:,1)= q; data(:,2) = I;
%                   q_range    -->  Restrict q_range(1)<=q<=q_range(2)
%
%       Outputs - 
%                   Pair Correlation function p(r) --> r(j) and p(j)
%
%   Simply attempts direct inverse FFT of data.

function [r,p] = Brute_PCF(data_in, q_range)

% Cut the data just to the allowed q_range;
temp = length(data_in); jmin = 1;
while ((jmin<temp)&(data_in(jmin,1)<q_range(1)))
    jmin=jmin+1;
end
jmax=jmin;
while ((jmax<temp)&(data_in(jmax,1)<q_range(2)) )
    jmax = jmax+1;
end
data = data_in([jmin:jmax],:);

% Set up bins for p
Nbins = 500; 
R_max = 250;
r = ([1:Nbins]-0.5)* R_max/Nbins;
p = zeros(size(r));
Iq = data(:,2).*data(:,1);
q = data(:,1);
Nq = length(Iq);

% Do the inverse ft.
for j=1:Nbins
    for k=1:Nq
        p(j) = p(j) + Iq(k) * sin( q(k) * r(j));
    end
end
p = p .*r;
p = p /( sum(abs(p)) * (r(2)-r(1)));