PROGRAM d10r4(input,output);
(* driver for routine DBRENT *)

(*$I MODFILE.PAS *)

CONST
   tol = 1.0e-6;
   eql = 1.0e-4;
TYPE
   RealArray20 = ARRAY [1..20] OF real;
VAR
   ax,bx,cx,fa,fb,fc,xmin,dbr: real;
   i,iflag,j,nmin: integer;
   amin: RealArray20;

(*$I BESSJ1.PAS *)

FUNCTION dfunc(x: real): real;
BEGIN
   dfunc := -bessj1(x)
END;

(*$I BESSJ0.PAS *)

FUNCTION func(x: real): real;
BEGIN
   func := bessj0(x)
END;

(*$I MNBRAK.PAS *)

(*$I DBRENT.PAS *)

BEGIN
   nmin := 0;
   writeln;
   writeln('minima of the function bessj0');
   writeln('min. #':10,'x':8,
      'bessj0(x)':16,'bessj1(x)':12,'DBRENT':11);
   FOR i := 1 TO 100 DO BEGIN
      ax := i;
      bx := i+1.0;
      mnbrak(ax,bx,cx,fa,fb,fc);
      dbr := dbrent(ax,bx,cx,tol,xmin);
      IF nmin = 0 THEN BEGIN
         amin[1] := xmin;
         nmin := 1;
         writeln(nmin:7,xmin:15:6,func(xmin):12:6,
            dfunc(xmin):12:6,dbr:12:6);
      END ELSE BEGIN
         iflag := 0;
         FOR j := 1 TO nmin DO
            IF abs(xmin-amin[j]) <= eql*xmin THEN
               iflag := 1;
         IF iflag = 0 THEN BEGIN
            nmin := nmin+1;
            amin[nmin] := xmin;
            writeln(nmin:7,xmin:15:6,func(xmin):12:6,
               dfunc(xmin):12:6,dbr:12:6)
         END
      END
   END
END.