GSL containers (switched sparse format to binary trees)

[Gerard Jungman]

As before, I apologize for the flood of messages.
But I figure better a few shorter messages than
one long message with multiple sub-topics.

Here is another discussion that I found interesting:

   http://comments.gmane.org/gmane.comp.lib.gsl.general/4385

As usual, the details could be debated. But I found the
following quote to be very telling:

  "Rhys, I did try to use views. They do not help because the
   gsl routines allocate vectors internally and there is not
   much that I can do about it... except for maybe hacking
   gsl and changing gsl_vector_alloc myself."

People seem to be led to this conclusion from multiple
directions.

Another choice quote:

   "The other issue is: the implementation of gsl_vector just
    seems inefficient to me. Looking at the code, it seems like
    a single vector requires 3 calls to malloc and free (one for
    the data, one for the gsl_block, and one for the gsl_vector
    itself). The manual states that the block is there for
    "consistency", and I can see how memory management becomes
    easier with it. But it seems to be a case of generality at
    the expense of performance. Also, the stride and the owner
    flag are part of the gsl_vector object to make it work with
    gsl_views, but then people who never need views pay the
    performance price anyway."