zbrac.pas

来自「Delphi Pascal 数据挖掘领域算法包 数值算法大全」· PAS 代码 · 共 31 行

PROCEDURE zbrac(VAR x1,x2: real; VAR succes: boolean);
(* Programs using routine ZBRAC must externally define a
function fx(x:real):real which is to be bracketed. *)
LABEL 99;
CONST
   factor=1.6;
   ntry=50;
VAR
   j: integer;
   f2,f1: real;
BEGIN
   IF (x1 = x2) THEN BEGIN
      writeln('pause in routine ZBRAC');
      writeln('you have to guess an initial range'); readln
   END;
   f1 := fx(x1);
   f2 := fx(x2);
   succes := true;
   FOR j := 1 TO ntry DO BEGIN
      IF (f1*f2 < 0.0) THEN GOTO 99;
      IF (abs(f1) < abs(f2)) THEN BEGIN
         x1 := x1+factor*(x1-x2);
         f1 := fx(x1)
      END ELSE BEGIN
         x2 := x2+factor*(x2-x1);
         f2 := fx(x2)
      END
   END;
   succes := false;
99:   END;