betai.pas

Delphi Pascal 数据挖掘领域算法包 数值算法大全

FUNCTION betai(a,b,x: real): real;
VAR
   bt: real;
BEGIN
   IF ((x < 0.0) OR (x > 1.0)) THEN BEGIN
      writeln('pause in routine BETAI'); readln
   END;
   IF ((x = 0.0) OR (x = 1.0)) THEN bt := 0.0
   ELSE bt := exp(gammln(a+b)-gammln(a)-gammln(b)
           +a*ln(x)+b*ln(1.0-x));
   IF (x < ((a+1.0)/(a+b+2.0))) THEN
      betai := bt*betacf(a,b,x)/a
   ELSE betai := 1.0-bt*betacf(b,a,1.0-x)/b
END;