Updated documentation around optional input 'args'

Author: lindonroberts

docs/userguide.rst

@@ -72,7 +72,7 @@ The :code:`solve` function has several optional arguments which the user may pro
 
 These arguments are:
 
-* :code:`args` - a tuple of extra arguments passed to the objective function
+* :code:`args` - a tuple of extra arguments passed to the objective function. This feature is new, and not yet avaiable in the PyPI version of Py-BOBYQA; instead, use Python's built-in function :code:`lambda`.
 * :code:`bounds` - a tuple :code:`(lower, upper)` with the vectors :math:`a` and :math:`b` of lower and upper bounds on :math:`x` (default is :math:`a_i=-10^{20}` and :math:`b_i=10^{20}`). To set bounds for either :code:`lower` or :code:`upper`, but not both, pass a tuple :code:`(lower, None)` or :code:`(None, upper)`.
 * :code:`npt` - the number of interpolation points to use (default is :code:`2*len(x0)+1`). Py-BOBYQA requires :code:`n+1 <= npt <= (n+1)*(n+2)/2` for a problem with :code:`len(x0)=n`. Larger values are particularly useful for noisy problems.
 * :code:`rhobeg` - the initial value of the trust region radius (default is :math:`0.1\max(\|x_0\|_{\infty}, 1)`).