function I = at(x,t)% AT  Return element index corresponding to a time value.%% I = AT(X,T)  Return element index I at time location t in signal% object X.% $Id: at.m 119 2006-09-26 12:28:25Z mairas $%I = at(x.time.t,t);I = round(x.time.fs*(t-x.time.begin))+1;