The goal of cryptocurrencies is decentralization. In principle, all currencies have equal status. Unlike traditional stock markets, there is no default currency of denomination (fiat), thus the trading pairs can be set freely. However, it is impractical to set up a trading market between every two currencies. In order to control management costs and ensure sufficient liquidity, we must give priority to covering those large-volume trading pairs and ensure that all coins are reachable. We note that this is an optimization problem. Its particularity lies in: 1) the trading volume between most (>99.5%) possible trading pairs cannot be directly observed. 2) It satisfies the connectivity constraint, that is, all currencies are guaranteed to be tradable. To solve this problem, we use a two-stage process: 1) Fill in missing values based on a regularized, truncated eigenvalue decomposition, where the regularization term is used to control what extent missing values should be limited to zero. 2) Search for the optimal trading pairs, based on a branch and bound process, with heuristic search and pruning strategies. The experimental results show that: 1) If the number of denominated coins is not limited, we will get a more decentralized trading pair settings, which advocates the establishment of trading pairs directly between large currency pairs. 2) There is a certain room for optimization in all exchanges. The setting of inappropriate trading pairs is mainly caused by subjectively setting small coins to quote, or failing to track emerging big coins in time. 3) Too few trading pairs will lead to low coverage; too many trading pairs will need to be adjusted with markets frequently. Exchanges should consider striking an appropriate balance between them.

翻译：加密货币的目标是实现去中心化。原则上，所有货币具有同等地位。与传统股票市场不同，不存在默认的计价法币，因此交易对可以自由设定。然而，在每两种货币之间建立交易市场是不切实际的。为控制管理成本并确保足够流动性，必须优先覆盖高交易量的交易对，同时保证所有币种可达。我们注意到这是一个优化问题，其特殊性在于：1）绝大多数（>99.5%）可能交易对的交易量无法直接观测；2）需满足连通性约束，即确保所有币种可交易。为解决该问题，我们采用两阶段流程：1）基于带正则化的截断特征值分解填补缺失值，通过正则化项控制缺失值归零的程度；2）基于分支定界过程搜索最优交易对，结合启发式搜索与剪枝策略。实验结果表明：1）当计价币种数量不受限时，将得到更去中心化的交易对设置，这支持直接建立大币种间的交易对；2）所有交易所均存在一定优化空间，不当交易对设置主要由主观设定小币种计价或未能及时追踪新兴大币种导致；3）交易对过少将导致覆盖率低，过多则需频繁随市场调整。交易所应在两者间寻求适当平衡。