unit2.pas

来自「1、说明： 本书中所有的常用数值算法子过程按书中的章数分别放在以C开头」· PAS 代码 · 共 53 行

unit Unit2;

interface
uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms,unit1, Dialogs;

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