[Bug-gsl] Minor but still obvious stylistic concerns in BFGS minimization routines

[Alan W. Irwin]

Version gsl-1.7:

(1) directional_minimize.c in the minimize routine:

double iter = 0;

should be changed to

int iter = 0;

Some of the type double comparisons made later in the routine are compared
to 0 rather than 0.

These changes should speed up the routine (since casts are avoided).
I imagine the effect is minute, and possibly not even measurable so that
is why I classify these issues as merely a stylistic concern.

(2) vector_bfgs.c:

The method is incorrectly classified in a few places as a conjugate gradient
method rather than the appropriate classification which is a quasi-Newton
method.  This incorrect classificiation could cause some misunderstandings
for people unfamiliar with minimization methods.

Here are my suggested changes:

(a) In one comment

conjugate gradient method ==> quasi-Newton method

(b) In two output messages:
conjugate direction ==> direction

(3) This same confusion also occurs in
http://www.network-theory.co.uk/docs/gslref/gsl-ref_467.html when the method
is described as follows:

"This is the vector Broyden-Fletcher-Goldfarb-Shanno (BFGS) conjugate
gradient algorithm. It is a quasi-Newton method which builds up an
approximation to the second derivatives of the function f using the
difference between successive gradient vectors."

I think "conjugate gradient" should be dropped from that first sentence.

These are all extremely minor nit-picks, but nevertheless, it would be nice
to get these issues cleaned up.

Alan
__________________________
Alan W. Irwin

Astronomical research affiliation with Department of Physics and Astronomy,
University of Victoria (astrowww.phys.uvic.ca).

Programming affiliations with the FreeEOS equation-of-state implementation
for stellar interiors (freeeos.sf.net); PLplot scientific plotting software
package (plplot.org); the Yorick front-end to PLplot (yplot.sf.net); the
Loads of Linux Links project (loll.sf.net); and the Linux Brochure Project
(lbproject.sf.net).
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