unit2.pas

《Delphi常用数值算法集》的配书源码

unit Unit2;

interface
uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms,unit1, Dialogs;
procedure TRAPZD(A, B:real;var S:real; N:integer);
procedure QSIMP(A, B:real;var S:real);

implementation
procedure TRAPZD(A, B:real;var S:real; N:integer);
var
    J,IT:integer;
    TNM,DEL,X,SUM:real;
begin
    If N = 1 Then
    begin
        S:=0.5 * (B - A) * (FUNC(A) + FUNC(B));
        IT:=1;
    end
    Else
    begin
        IT:=Trunc(exp((N - 2)*Ln(2)));
        TNM:=IT;
        DEL:=(B - A) / TNM;
        X:=A + 0.5 * DEL;
        Sum:=0;
        For J:=1 To IT do
        begin
            Sum:=Sum + FUNC(X);
            X:=X + DEL;
        end;
        S:=0.5 * (S + (B - A) * Sum / TNM);
    end;
end;

procedure QSIMP(A, B:real; var S:real);
const
    EPS = 0.000001;    JMAX = 20;
var
    J:integer;  OST,OS,ST:real;
begin
    OST:=-1E+30;
    OS:=-1E+30;
    For J:=1 To JMAX do
    begin
        TRAPZD(A, B, ST, J);
        S:=(4 * ST - OST) / 3;
        If Abs(S - OS) < EPS * Abs(OS) Then Exit;
        OS:=S;
        OST:=ST;
    end;
    ShowMessage('Too many steps.');
end;
end.