Each field name in the data is considered either a numeric field or an
alphanumeric field.
Each numeric field becomes a Matlab data vector,
with the field name as the vector name.
Each alphanumeric field becomes
a Matlab character array, with the field name as the array name.
The algorithm used to make the numeric/alphanumeric decision is weak.
Accordingly, its results may be presented to you for correction before
the Matlab file is made.
Invalid entries in a numeric vector (including the JGOFS system missing
data code 'nd') are given a Matlab NaN value.
Character array values
are unchanged, which means that missing character values retain the
JGOFS system missing data code 'nd'.
The names of files produced have a .mat extension