two successive letters (especially two letters used to represent a single sound: `sh' in `shoe')
双语例句
Digraphs have a simple pictorial representation. 有向图有简单的图形表示。
Using matrix theory, we present a sharp upper bound on the spectral radius of digraphs and strongly connected diagraphs. 摘要利用矩阵理论，给出了简单有向图的谱半径可达上界和强连通有向图的谱半径上界。
