gser.txt

用于开发税务票据管理的软件

procedure GSER(var GAMSER:real; A:real; X:real; var GLN:real);
label 1;
const
  ITMAX=100;    EPS=0.3E-6;
var
  N:Integer;
  SUM,DEL,AP:Real;
begin
  GLN:=GAMMLN(A);
  If X <= 0 Then
    If X < 0 Then
    begin
        ShowMessage('警告：X<0，退出程序。');
        goto 1;
    end
  else
  begin
      GAMSER:=0;
      goto 1;
  end;
  AP:=A;
  SUM:=1 / A;
  DEL:=SUM;
  For N:=1 To ITMAX do
  begin
      AP:=AP + 1;
      DEL:=DEL * X / AP;
      SUM:=SUM + DEL;
      If Abs(DEL) < Abs(SUM) * EPS Then GoTo 1;
  end;
  ShowMessage('A too large, ITMAX too small');
1: GAMSER:=SUM * Exp(-X + A * Ln(X) - GLN);
end;