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;