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## B.42 `tmatchn`: Crossmatches multiple tables using flexible criteria

`tmatchn` performs efficient and flexible crossmatching between multiple tables. It can match rows on the basis of their relative position in the sky, or alternatively using many other criteria such as separation in in some isotropic or anisotropic Cartesian space, identity of a key value, or some combination of these; the full range of match criteria is dicussed in Section 7.1.

Since the match criteria define what counts as a match between two objects, it is not immediately obvious what is meant by a multi-table match. In fact the command can work in one of two distinct modes, controlled by the `multimode` parameter. In `pairs` mode, one table (by default the first input table) is designated the reference table, and pair matches between each of the other tables and that one are identified. In `group` mode groups of objects from all the input tables are identified, as discussed in Section 7.2. Currently, in both cases an output matched row cannot contain more than one object from each input table. Options for output of multiple rows per input table per match may be forthcoming in future releases if there is demand.

`tmatchn` is intended for use with more than two input tables - see `tmatch1` and `tmatch2` for 1- and 2-table crossmatching respectively.

- B.42.1 Usage
- B.42.2 Examples

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STILTS - Starlink Tables Infrastructure Library Tool Set
Starlink User Note256
STILTS web page: http://www.starlink.ac.uk/stilts/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@jiscmail.ac.uk