用于开发税务票据管理的软件

				unit Unit1;
				
				interface
				
				uses
				  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
				  StdCtrls;
				procedure DERIVS(X:real; Y:array of real;var DYDX:array of real);
				type
				  TForm1 = class(TForm)
				    Button1: TButton;
				    Memo1: TMemo;
				    procedure Button1Click(Sender: TObject);
				  private
				    { Private declarations }
				  public
				    { Public declarations }
				  end;
				
				var
				  Form1: TForm1;
				
				implementation
				//PROGRAM D12R1
				//Driver for routine RK4
				uses
				  unit2;
				  {$R *.DFM}
				procedure DERIVS(X:real; Y:array of real;var DYDX:array of real);
				begin
				    DYDX[1]:= -Y[2];
				    DYDX[2]:= Y[1] - (1 / X) * Y[2];
				    DYDX[3]:= Y[2] - (2 / X) * Y[3];
				    DYDX[4]:= Y[3] - (3 / X) * Y[4];
				end;
				procedure TForm1.Button1Click(Sender: TObject);
				const
				  s1='%12.6f';  N = 4;
				var
				  F:TextFile;
				  Y,DYDX,YOUT:array[0..N] of real;  I,J:integer;   X,H:real;
				begin
				  X:=1;
				  Y[1]:=BESSJ0(X);
				  Y[2]:=BESSJ1(X);
				  Y[3]:=BESSJ(2, X);
				  Y[4]:=BESSJ(3, X);
				  DYDX[1]:=-Y[2];
				  DYDX[2]:=Y[1] - Y[2];
				  DYDX[3]:=Y[2] - 2* Y[3];
				  DYDX[4]:=Y[3] - 3* Y[4];
				  //输出计算结果到文件
				  AssignFile(F, 'd:\delphi_shu\p12\d12r1.dat');
				  Rewrite(F);
				  Writeln(F);
				  Writeln(F,'Bessel Function:     J0          J1          J2         J3');
				  For I:=1 To 5 do
				  begin
				    H:=0.2 * I;
				    RK4(Y, DYDX, N, X, H, YOUT);
				    Writeln(F);
				    Writeln(F,'For a step size of: ', Format('%4.2f',[H]));
				    Writeln(F,'      RK4:    ',Format(s1,[YOUT[1]]),Format(s1,[YOUT[2]]),
				               Format(s1,[YOUT[3]]),Format(s1,[YOUT[4]]));
				    Writeln(F,'      Actual: ',Format(s1,[BESSJ0(X + H)]),
				               Format(s1,[BESSJ1(X + H)]),Format(s1,[BESSJ(2, X + H)]),
				               Format(s1,[BESSJ(3, X + H)]));
				  end;
				  CloseFile(F);
				  //屏幕显示计算结果
				  memo1.Lines.LoadFromFile('d:\delphi_shu\p12\d12r1.dat');
				end;
				
				end.