function u_inf = u_m_inf_put(x,tau,k)
% U_M_INF_PUT - the transformed boundary condition at x=-\infty for a put 
% 
% Checked: 2008-11-16 ... no errors found 
%   
% Written by:
% -- 
% John L. Weatherwax                2008-06-11
% 
% email: wax@alum.mit.edu
% 
% Please send comments and especially bug reports to the
% above email address.
% 
%-----

u_inf = exp( 0.25*((k+1)^2)*tau ) * exp( 0.5*(k-1)*x ) * exp( -k*tau );