betacf.txt

来自「1.г函数、贝塔函数、阶乘及二项式系数 2.不完全г函数、误差函数 3.不完」· 文本 代码 · 共 37 行

Function BETACF( A, B, X:real):real;
label 1;
const
  ITMAX=100;    EPS=0.0000003;
var
  TEM,QAP,QAM,QAB,EM,D:REAL; BZ,BP,BPP,BM,AZ,AAP:REAL;
  AM,AOLD,AP:REAL;
  M:INTEGER;
begin
  AM:=1;
  BM:=1;
  AZ:=1;
  QAB:=A + B;
  QAP:=A + 1;
  QAM:=A - 1;
  BZ:=1 - QAB * X / QAP;
  For M:=1 To ITMAX DO
  begin
    EM:=M;
    TEM:=EM + EM;
    D:=EM * (B - M) * X / ((QAM + TEM) * (A + TEM));
    AP:=AZ + D * AM;
    BP:=BZ + D * BM;
    D:=-(A + EM) * (QAB + EM) * X / ((A + TEM) * (QAP + TEM));
    AAP:=AP + D * AZ;
    BPP:=BP + D * BZ;
    AOLD:=AZ;
    AM:=AP / BPP;
    BM:=BP / BPP;
    AZ:=AAP / BPP;
    BZ:=1;
    If Abs(AZ - AOLD) < EPS * Abs(AZ) Then GoTo 1;
  end;
  ShowMessage('A or B too big, or ITMAX too small');
  exit;
1: BETACF:=AZ;
end;