suggestions for improving GSL

[Brook Milligan <brook at biology dot nmsu dot edu>]

As a user of the GSL, I have a few suggestions of areas where
enhancement would be really useful.

- add an appropriate set of covariance functions to the statistics
  support; these would be exactly analogous to the several variance
  functions, but would take as arguments 2 (not 1) list of values.  In
  fact, the variance functions could be written to simply call the
  covariance functions with suitable arguments.

- add multidimensional minimization to the set of optimization
  functions.  A candidate that I have found useful and easy to
  implement is described in Press, William H. and Teukolsky, Saul
  A. and Vetterling, William T. and Flannery, Brian P.
  1992. Numerical Recipies in C. The art of scientific computing.
  Second Edition.  Cambridge University Press, New York, New York.
  Section 10.4. Downhill simplex method in multidimensions. Pages
  408-412.  That might be a good start, though Press et al. also
  provide other ideas that could be added as well.  Note that if this
  is done, some capability (e.g., another function in addition to the
  one to be minimized) is required to specify whether points are
  within the domain of the function to be minimized; the published
  algorithm simply assumes that the domain extends throughout the
  entire N-dimensional space.

- add extern "C" { ... } to the header files so that other languages
  can be easily used in conjunction with the GSL.

Please consider these ideas.  I think they would provide a significant
enhancement of the utility of the GSL.

Thanks.

Cheers,
Brook