rtnewt.pas

来自「Delphi Pascal 数据挖掘领域算法包 数值算法大全」· PAS 代码 · 共 27 行

FUNCTION rtnewt(x1,x2,xacc: real): real;
(* Programs using routine RTNEWT must externally define procedure
funcd(x,f,df:real) which returns the function value f and its
derivative df at the point x. *)
LABEL 99;
CONST
   jmax=20;
VAR
   df,dx,f,rtn: real;
   j: integer;
BEGIN
   rtn := 0.5*(x1+x2);
   FOR j := 1 TO jmax DO BEGIN
      funcd(rtn,f,df);
      dx := f/df;
      rtn := rtn-dx;
      IF ((x1-rtn)*(rtn-x2) < 0.0) THEN BEGIN
         writeln('pause in routine RTNEWT');
         writeln('jumped out of brackets'); readln
      END;
      IF (abs(dx) < xacc) THEN GOTO 99
   END;
   writeln('pause in routine RTNEWT');
   writeln('maximum number of iterations exceeded'); readln;
99:   rtnewt := rtn
END;