用于开发税务票据管理的软件

				Function RTFLSP(X1, X2, XACC:real):real;
				Label 99;
				var
				    XL,XH,SWAP,FL,FH,RTF,DX,F,DEL:real;  J,MAXIT:integer;
				begin
				    MAXIT:=30;
				    FL:=FUN(X1);
				    FH:=FUN(X2);
				    If FL * FH > 0 Then
				        ShowMessage('Root must be bracketed for false position');
				    If FL < 0 Then
				    begin
				        XL:=X1;
				        XH:=X2;
				    end
				    Else
				    begin
				        XL:=X2;
				        XH:=X1;
				        SWAP:=FL;
				        FL:=FH;
				        FH:=SWAP;
				    end;
				    DX:=XH - XL;
				    For J:=1 To MAXIT do
				    begin
				        RTF:=XL + DX * FL / (FL - FH);
				        F:=FUN(RTF);
				        If F < 0 Then
				        begin
				            DEL:=XL - RTF;
				            XL:=RTF;
				            FL:=F;
				        end
				        Else
				        begin
				            DEL:=XH - RTF;
				            XH:=RTF;
				            FH:=F;
				        end;
				        DX:=XH - XL;
				        If (Abs(DEL) < XACC) Or (F = 0) Then goto 99;
				    end; 
				    ShowMessage('RTFLSP exceed maximum iterations');
				99: RTFLSP:=RTF;
				end;