% -*- texinfo -*-
% @deftypefn {Function File} {} starp (@var{P}, @var{K}, @var{ny}, @var{nu})
%
% Redheffer star product or upper/lower LFT, respectively.
% @example
% @group
%
% +-------+
% --------->| |--------->
% | P |
% +--->| |---+ ny
% | +-------+ |
% +-------------------+
% | |
% +----------------+ |
% | |
% | +-------+ |
% +--->| |------+ nu
% | K |
% --------->| |--------->
% +-------+
% @end group
% @end example
% If @var{ny} and @var{nu} ``consume'' all inputs and outputs of
% @var{K} then the result is a lower fractional transformation.
% If @var{ny} and @var{nu} ``consume'' all inputs and outputs of
% @var{P} then the result is an upper fractional transformation.
%
% @var{ny} and/or @var{nu} may be negative (i.e. negative feedback).
% @end deftypefn