With the exception of lbfgsb.c (see below), the sources here are 
derived from the Minpack distribution, at

http://www.netlib.org/minpack/

The Minpack Copyright Notice is reproduced below.

One modification has been made for use with gretl: all the
included minpack functions that invoke "callback" functions
have had an extra argument added (in the last position),
namely a general-purpose void pointer that can be used to
pass additional data to the callback.  The signature of
the callbacks therefore also has an additional "void *"
parameter. 

The file lbfgsb.c is an f2c translation of the fortran code
routines.f from L-BFGS-B, at

http://www.ece.northwestern.edu/~nocedal/lbfgsb.html

L-BFGS-B References:

R. H. Byrd, P. Lu and J. Nocedal. A Limited Memory Algorithm 
for Bound Constrained Optimization, (1995), SIAM Journal on 
Scientific and Statistical Computing , 16, 5, pp. 1190-1208.

C. Zhu, R. H. Byrd and J. Nocedal. L-BFGS-B: Algorithm 778: 
L-BFGS-B, FORTRAN routines for large scale bound constrained 
optimization (1997), ACM Transactions on Mathematical Software, 
Vol 23, Num. 4, pp. 550 - 560.

====
 
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