Format of CSV correlation/covariance files:
ZZIAAA = Z x 10000 + I x 1000 + A, for each isotope
, ZZIAAA_0, ZZIAAA_1, ZZIAAA_2, ...
ZZIAAA_0, VAR(0), CO(0,1), CO(0,2), ...
ZZIAAA_1, CO(1,0), VAR(1), CO(1,2), ...
ZZIAAA_2, CO(2,0), CO(2,1), VAR(2), ...
. , . , . , . , ...
. , . , . , . , ...
. , . , . , . , ...