gser.pas

Delphi Pascal 数据挖掘领域算法包 数值算法大全

PROCEDURE gser(a,x: real; VAR gamser,gln: real);
LABEL 1;
CONST
   itmax=100;
   eps=3.0e-7;
VAR
   n: integer;
   sum,del,ap: real;
BEGIN
   gln := gammln(a);
   IF (x <= 0.0) THEN BEGIN
      IF (x < 0.0) THEN BEGIN
         writeln('pause in GSER - x less than 0'); readln
      END;
      gamser := 0.0
   END ELSE BEGIN
      ap := a;
      sum := 1.0/a;
      del := sum;
      FOR n := 1 TO itmax DO BEGIN
         ap := ap+1.0;
         del := del*x/ap;
         sum := sum+del;
         IF (abs(del) < abs(sum)*eps) THEN GOTO 1
      END;
      writeln('pause in GSER - a too large, itmax too small'); readln;
1:      gamser := sum*exp(-x+a*ln(x)-gln)
   END
END;