including outside code in octave

[Tommy Guy]

I have been examining ways to fix the logm function, which currently
uses an eigenvalue decomposition and is unstable.  See the help-octave
email list for a discussion.

As a new developer with limited time (graduate student...) I am taking
a two pronged approach.  First, I will write a .m algorithm that is an
improvement.  I will then work on porting it to native code along with
a few other improvements (once I get the code compiled :) )

My questions is as follows.  First, in reading up on matrix
logarithms, I came across some code that is available under GPL 3.0.
The code is at (http://www.maths.manchester.ac.uk/~higham/mftoolbox/).
 I am modifying this code a good deal, but is it legal to include code
under the GPL 3.0 license in Octave?  My understanding is yes, but I
want to be sure.

Tommy Guy