The Dow Jones Industrial Average ended the week on a high note, capping the third straight week of gains for the S&P 500 and the Nasdaq. Now that many companies have undergone difficult periods of restructuring, investors expect to see stronger economic growth, according to analysts. Meanwhile, ad-stock activity was mostly uneventful, except for unusually large trading volume surrounding IPG (see story on page 8). On the Big Board, IPG shares climbed 8.2 percent to close at $15.15, and Omnicom increased 1.4 percent to $77.89. British holding company WPP, trading as American Depository Receipts on the Nasdaq, rose 0.4 percent to $45.89.