Designing proxies for stock market indices is computationally hard*
研究了基于历史数据为股票市场指数设计代理变量（投资组合）的问题，发现四种指数与三种标准组合的十一种情况下，该问题都是NP难的，即很可能无法高效求解。
In this paper, we study the problem of designing proxies (or portfolios) for various stock market indices based on historical data. We use four different methods for computing market indices, all of which are formulae used in actual stock market analysis. For each index, we consider three criteria for designing the proxy: the proxy must either track the market index, outperform the market index, or perform within a margin of error of the index while maintaining a low volatility. In eleven of the twelve cases (all combinations of four indices with three criteria except the problem of sacrificing return for less volatility using the price-relative index) we show that the problem is NP-hard, and hence most likely intractable.