function pdf=dfgamma(lamda, r, samples) 
% dfgamma(lamda, r, samples)  Generates a gamma pdf with parameter r. 
%    samples sets the size of the numerical representation, and is optional. 
%    The default sample size is 1000. 
if nargin==2 
   samples=1000; 
end 
if r<=0 
   error('invalid value for r') 
end 
V=sqrt(r)/lamda; 
X=5*V; 
while lamda/gamma(r)*((lamda*X)^(r-1))*exp(-lamda*X) > 1e-6 
   X=X+V; 
end 
x=[0:X/samples:X]; 
p=(lamda/gamma(r)).*((lamda*x).^(r-1)).*exp(-lamda*x); 
pdf=[0 1; x' p']; 
if ispf(pdf)==0 
   p=p./ttlprob(pdf); 
   pdf=[0 1; x' p']; 
end