data access

[Jason Stover]

I'm wrestling with reading data via casefiles again. We've all said
it would be nice to make reading the data easier, and Ben has
complained about every procedure's need to pass the entire data
set. 

I thought of what might be a simple approach: Each time a procedure
reads the data via casefiles, it stores them in a gsl_matrix, along
with some other information about variable names, etc. Then the next
time a procedure needs the data, it uses that gsl_matrix, if it's
available and contains the necessary information. If not, it reads the
data via casefiles.

Filling up and using a gsl_matrix is easy. I don't know how easy it
would be to store the meta-data the procedures would need.

Pardon me if this is an old idea. But the difficulty of using
casefiles prevents other people from contributing mathematical code,
whereas gsl_matrices are easy to handle.

-Jason