lib/distribution/binomial/ruby.rb in distribution-0.4.0 vs lib/distribution/binomial/ruby.rb in distribution-0.5.0

@@ -1,11 +1,12 @@
 module Distribution
   module Binomial
     module Ruby_
       class << self
         def pdf(k,n,pr)
-          Math.binomial_coefficient(n,k)*(pr**k)*(1-pr)**(n-k)          
+          raise "k>n" if k>n
+	  Math.binomial_coefficient(n,k)*(pr**k)*(1-pr)**(n-k)          
         end
         def cdf(k,n,pr)
           #(0..x.floor).inject(0) {|ac,i| ac+pdf(i,n,pr)}
           Math.regularized_beta_function(1-pr,n - k,k+1)
         end
@@ -22,6 +23,6 @@
         
         alias :exact_pdf :pdf 
       end
     end
   end
-end
\ No newline at end of file
+end