function r=cubici1(fnew,fold,graddnew,graddold,stepsize)
%CUBICI1 Cubicly interpolates 2 points and gradients to estimate minimum.
%
%   This function uses cubic interpolation and the values of two 
%   points and their gradients in order to estimate the minimum of a 
%   a function along a line.

%   Copyright (c) 1990-98 by The MathWorks, Inc.
%   $Revision: 1.9 $  $Date: 1997/11/29 01:23:01 $
%   Andy Grace 7-9-90.

if isinf(fnew), fnew=1/eps; end
z=3*(fold-fnew)/stepsize+graddold+graddnew;
w=real(sqrt(z*z-graddold*graddnew));
r=stepsize*((z+w-graddold)/(graddnew-graddold+2*w));