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{ ******************************************************************
Binomial distribution
****************************************************************** }
unit ubinom;
interface
uses
utypes, umath;
function Binomial(N, K : Integer) : Float;
{ Binomial coefficient C(N,K) }
function PBinom(N : Integer; P : Float; K : Integer) : Float;
{ Probability of binomial distribution }
implementation
function Binomial(N, K : Integer) : Float;
var
I, N1 : Integer;
Prod : Float;
begin
SetErrCode(FOk);
if K < 0 then
Binomial := 0.0
else if (K = 0) or (K = N) then
Binomial := 1.0
else if (K = 1) or (K = N - 1) then
Binomial := N
else
begin
if K > N - K then K := N - K;
N1 := Succ(N);
Prod := N;
for I := 2 to K do
Prod := Prod * ((N1 - I) / I);
Binomial := Int(0.5 + Prod);
end;
end;
function PBinom(N : Integer; P : Float; K : Integer) : Float;
begin
SetErrCode(FOk);
if (P < 0.0) or (P > 1.0) or (N <= 0) or (N < K) then
PBinom := DefaultVal(FDomain, 0.0)
else if K = 0 then
PBinom := Power(1.0 - P, N)
else if K = N then
PBinom := Power(P, N)
else
PBinom := Binomial(N, K) * Power(P, K) * Power(1.0 - P, N - K);
end;
end.
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