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;