# Groups¶

Groups are lists of matrix names and we use them to categorize matrices in Matrix Depot. The list below shows all the predefined groups in Matrix Depot and we can extend this list by defining new groups. Group names are noted as symbols, e.g. :symmetric.

## Predefined Groups¶

- all
- All the matrices in the collection.
- data
- The matrix has been downloaded from UF sparse matrix collection or the Matrix Market collection.
- eigen
- Part of the eigensystem of the matrix is explicitly known.
- graph
- An adjacency matrix of a graph.
- illcond
- The matrix is ill-conditioned for some parameter values.
- inverse
- The inverse of the matrix is known explicitly.
- posdef
- The matrix is positive definite for some parameter values.
- random
- The matrix has random entries.
- regprob
- The output is a test problem for Regularization Methods.
- sparse
- The matrix is sparse.
- symmetric
- The matrix is symmetric for some parameter values.

## Adding New Groups¶

New groups can be added with the macro `@addgroup`

:

```
@addgroup myfav = ["lehmer", "cauchy", "hilb"]
@addgroup test_for_paper2 = ["tridiag", "sampling", "wing"]
listgroups()
Groups:
data eigen illcond inverse
posdef random regprob sparse
symmetric myfav test_for_paper2
listnames(:myfav)
3-element Array{ASCIIString,1}:
"lehmer"
"cauchy"
"hilb"
```