Westpac overcame a period of weak income growth in the six months to Match by cutting costs and reducing impairment charges. In a result similar to ANZ's, which was announced early last week, Westpac's bottom line performance is also the result of tighter discipline rather than growth.Westpac chief executive Gail Kelly has promised to maintain the bank's productivity drive.On Friday, Westpac reported a net profit of A$3.3 billion for the March half - up 11 per cent on the previous corresponding period, and up 10 per cent on the previous half.On the bank's preferred measure of cash earnings, its profit of $3.5 billion was 10 per cent up on the previous corresponding period.Net operating income, of $9.2 billion, was up four per cent on the previous corresponding period but was unchanged from the previous half. Business lending fell and Australian housing loans grew below system.Operating expenses were cut three per cent, from $4.01 billion in the September half of last year, to $3.9 billion in the latest half. The bank's cost-to-income ratio has fallen, from 44.1 per cent in March last year to 43.9 per cent in September and to 42.6 per cent in the latest half.Impairment charges fell from $608 million in March last year to $604 million in September and then to $438 million in the latest half. The ratio of impaired assets to total committed exposures fell from 58 basis points in the September half to 56 basis points in the latest half.Kelly told analysts on Friday: "The name of the game is maintaining discipline. The benefits you see this year flow from initiatives and work that we put into the system a year ago."The bank reported $121 million of productivity savings over the past six months. Westpac's chief financial officer, Phil Coffey, said these savings offset growth in wages, performance bonuses, annual rent reviews and marketing expenditure.Kelly said the bank had a number of "lean experts" working in different parts of the bank, helping re-design processes and make further improvements to efficiency. The bank also has a team working on projects to reduce the number of products the bank sells.Kelly said: "This is a very serious program of work that we've got that will carry us through for a few years to come."The prospects for growth do not look so bright. Kelly said she would be comfortable growing the mortgage book a little below system growth rate, which is around four per cent.