Slackware 13 and Octave 3.2
 

I installed Octave 3.2 for Slackware 12.2 on Slackware 13. Octave for 13 isn't available.
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Octave initially didn't run correctly. I did need to do one fix. Octave 3.2 for Slackware 12.2 needs libgfortran.so.2.0.0.
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The fix is (as root) to add a soft link from /usr/lib/libgfortran.so.3.0.0. to /usr/lib/libgfortran.so.2

$ ls -l /usr/lib/libgfortran.so.2
lrwxrwxrwx 1 root root 20 2009-09-16 12:31 /usr/lib/libgfortran.so.2 -> libgfortran.so.3.0.0
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Octave 3.2 for Slackware 12.2 is available from Slacky.eu at:
http://www.slacky.eu/aadm/pkgs/index.php?ver=6&pkg=1809
Note the dependencies, more dependent packages are needed.

There is an octave slackbuild for slackware 13 at slackbuilds.org