defining a structure for sparse matrices

[chrbertsch]

(From a Discussion with Mathworks at the FMI Advisory Committee Meeting)
For defining sparse matrices one typically uses several Integer and Float arrays, e.g. using the CSR (Compressed Sparse Row) format (https://en.wikipedia.org/wiki/Sparse_matrix)
We could define a grouping in this layered standard.

[HansOlsson]

Two points:

• In terms of readability sorted COO (row_idx, col_idx, value) is likely easier to understand than CSR. Does readability of XML matter? Does the external format impact performance if we use XML, or can one convert while reading/writing without any extra cost (assuming sorted)?
• Are we just defining the structure, or also the values, i.e. the full triplet or just row_idx, col_idx; or are we interested in both?