MATLAB Programming

6 Data Import and Export
Data Compression
MATLAB compresses the data that you savetoaMAT-file.Datacompression
can save you a significant amount of storage space when you are working with
large files or working over a network.
Data compression is optional, however, and you can disable it either for an
individual save operation, or for all of your MATLAB sessions. Use the -v6
option with the save function to turn off compression on a per-command basis:
save filename -v6
To disable data compression for all of your MATLAB sessions, open the
Preferences dialog, select General and then MAT-Files, and click the option
that is equivalent to the command save -v6. See General Preferences for
MATLAB in the Desktop Tools and Development Environment documentation
for more information.
Note You cannot read a compressed MAT-file with MATLAB versions earlier
thanVersion7.TowriteaMAT-filethatyouwillbeabletoreadwithoneof
these versions, save to the file with data compression disabled.
Information returned by the command whos -file is independent of whether
the variables in that file are compressed or not. The byte counts returned by
this command represent the number of bytes data occupies in the MATLAB
workspace, and not in the file the data was saved to.
Evaluating When to Compress. You should consider both data set size
and the type of data being saved when deciding whether or not to compress
the data you save to a file. The benefits of data compression are greater
when saving large data sets (over 3 MB), and are usually negligible with
smaller data sets. Data that has repeating patterns or more consistent values
compresses better than random data. Compressing data that has a random
pattern is not recommended as it slows down the performance of save and
load significantly, and offers little benefit in return.
In general, data compression and decompression slows down all save and
some load operations to some extent. In most cases, however, the resulting
reductioninfilesizeisworththeadditional time spent compressing or
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