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1.15 Linesearch, minimize a function along dx

Helptext:

[a,fx,nev] = line_min (f, dx, args, narg, h, nev_max) - Minimize f() along dx

INPUT ----------
f    : string  : Name of minimized function
dx   : matrix  : Direction along which f() is minimized
args : cell    : Arguments of f
narg : integer : Position of minimized variable in args.  Default=1
h    : scalar  : Step size to use for centered finite difference
approximation of first and second derivatives. Default=1E-3.
nev_max : integer : Maximum number of function evaluations.  Default=30

OUTPUT ---------
a    : scalar  : Value for which f(x+a*dx) is a minimum (*)
fx   : scalar  : Value of f(x+a*dx) at minimum (*)
nev  : integer : Number of function evaluations

(*) The notation f(x+a*dx) assumes that args == {x}.

Reference: David G Luenberger's Linear and Nonlinear Programming