InfinitySparseMatrix is a special class of distance specifications. Finite entries indicate possible matches, while infinite or NA entries indicated non-allowed matches. This data type can be more space efficient for sparse matching problems. Usually, users will create distance specification using match_on, caliper, or exactMatch. The ordering of units in an InfinitySparseMatrix is not guaranteed to be maintained after subsetting and/or other operations are performed.

## Slots

colnames

vector containing names for all control units. This will either be a character vector or NULL if units have no names

rownames

vector containing names for all treated units. This will either be a character vector or NULL if units have no names

cols

vector of integers corresponding to control units

rows

vector of integers corresponding to treated units

dimension

integer vector containing the number of treated and control units, in that order

call

function call used to create the InfinitySparseMatrix

match_on, caliper, exactMatch, fullmatch, pairmatch