Matagi suji
Matagi suji, or "straddle suji", is a form of discard reading. It states that, when a number tile is discarded early, nearby tiles become safer. But, when a number tile is discarded late (especially if the riichi declaration tile), nearby tiles become more dangerous.
- When a tile numbered 3-7 is discarded, the tiles within +/- 2 of that tile are affected by matagi suji.
- When a tile numbered 2 or 8 is discarded, the 1-4 or 6-9 tiles are affected by matagi suji.
Table
| Discard | Remaining in Hand | Matagi suji |
|---|---|---|
| 2 | 23 | 1-4 |
| 3 | 23 or 34 | 1-4, 2-5 |
| 4 | 34 or 45 | 2-5, 3-6 |
| 5 | 45 or 56 | 3-6, 4-7 |
| 6 | 56 or 67 | 4-7, 5-8 |
| 7 | 67 or 78 | 5-8, 6-9 |
| 8 | 78 | 6-9 |
Theory
Matagi suji relies on the power of a shape like "233" or "334". When a player has a "233", it is unlikely for them to discard a 3 early - turning "233" -> "23" - since it'd come at a loss of tile efficiency. So if a 3 is discarded early, it is less likely for them to have "23" (which waits on 1-4) or "34" (which waits on 2-5) remaining. Therefore, an early discarded 3 makes both 1-4 and 2-5 safer. Note: tiles towards the outside of a discarded tile (1 & 2 in this case) are much safer; tiles towards the inside are not much safer than a regular tile.
Conversely, it is more likely for a player to keep shapes like "233" until just before tenpai. So if a 3 is discarded as the riichi declaration tile, it is more likely for them to have a "23" or "34" remaining. This means a late discarded 3 makes 1-4 and 2-5 more dangerous.
Note: if the riichi declaration tile was a tsumogiri tile (discarded right after drawing it), then number tiles around the last tedashi (discarded from hand) tile are dangerous instead.
Effectiveness
"Tiles nearby the riichi declaration tile" are more dangerous. But, when folding, there usually isn't a need to consider matagi suji. A 4 discarded as a riichi declaration does make the 5 more dangerous, but a non-suji 5 is already very dangerous. It can make an impact when deciding whether to push or fold, though.
"Tiles outside of early discards" are relatively safe; about as safe as regular suji (but a bit less safe).
External links
- Matagi suji danger analysis on Path of Houou
- Matagi suji on Mahjong Gem