logtest.m

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function q=logtest(data,bins)
%chi-square testing for lognormal distribution
%Gayatrii Prabhu and P. M. Shankar
y=sort(data./mean(data)); %unity mean
sig=sqrt(log(std(y)^2+1)); %parameter sigma for lognormal
mu=-sig^2/2; %second parameter for lognormal

inter=max(y)-min(y); %interval for chi-square test 
intstep=inter/bins; %size of sub-interval
intval=[min(y):intstep:max(y)]; %samples at the sub-intervals
k=[zeros(1,bins)]; %number of samples in each sub-interval

%counting the samples in each sub-interval
for i=1:length(y)
   for j=1:bins
      if y(i)<=intval(j+1)
         k(j)=k(j)+1;
         break;
      end;
   end;
end;

Fy=logncdf(intval,mu,sig); %cdf at each sub-interval sample 

p=zeros(1,bins);
for i=1:bins
   p(i)=Fy(i+1)-Fy(i); %probabilities at the sub-interval samples
end;

np=p.*length(y);

q=0; 
for i=1:bins
   q = q + ((k(i)-np(i))^2)/np(i); %chi-square test statistic
end;