function y = cnd(x)
%  pr = cnd(nd)
% computes the probability that a variable will be less
%    than x standard deviations  
% example: pr = cnd(1.5) 

% copyright, 1995, William F. Sharpe
% wfsharpe@leland.stanford.edu
% this version Nov. 2, 1995

     if x > 0
           y = 0.5 + erf(x/sqrt(2))/2;
        else
           y = 0.5 - erf(-x/sqrt(2))/2;
     end