unit Unit2;

interface
uses
  Windows, Messages, SysUtils, Classes, Graphics,unit1, Controls, Forms, Dialogs;

Function FACTLN(N:INTEGER):real;
Function GAMMLN(xx:real):real;

implementation
Function GAMMLN(XX:real):real;
const
  STP=2.50662827465; HALF=0.5; ONE=1.0; FPF=5.5;
var
  X,TMP,SER:double;
  J:integer;
  COF:array[1..6] of double;
begin
  COF[1]:=76.18009173;      COF[2]:=-86.50532033;
  COF[3]:=24.01409822;      COF[4]:=-1.231739516;
  COF[5]:= 0.120858003e-2;  COF[6]:=-0.536382e-5;
  X:=XX-ONE;
  TMP:=X+FPF;
  TMP:=(X+HALF)*Ln(TMP)-TMP;
  SER:=ONE;
  For J:=1 To 6 do
  begin
      X:=X+ONE;
      SER:=SER+COF[J]/X
  end;
  GAMMLN:=TMP+Ln(STP*SER);
end;

Function FACTLN(N:integer):real;
var
    I:integer;
    A:array[1..100] of real;
begin
    For I:=1 To 100 do
      A[I]:=-1;
    If N < 0 Then  ShowMessage('警告：現在N<0，請修改程序');
    If N <= 99 Then
    begin
        If A[N + 1] < 0 Then A[N + 1]:=GAMMLN(N + 1);
        FACTLN:=A[N + 1];
    end
    Else
      FACTLN:=GAMMLN(N + 1);
end;

end.