EXPOKIT
's dmexp
-type functions deal with
sparse matrices. These have a lot of zeros, and thus can
be compressed into COO (coordinated list) format, which
is described here:
https://en.wikipedia.org/wiki/Sparse_matrix#Coordinate_list_.28COO.29
In EXPOKIT
and its wrapper functions, a
COO-formated matrix is input as 3 vectors (first two
integer, the third double):
ia = row number
ja = column number
a = value of
that cell in the matrix (skipping 0 cells)