function [y]=taper(x,nt,dt,t1,t2);
%
%   TAPER  Taper time series. 
%          TAPER(X,NT,DT,T1,T2) takes time series sampled at DT 
%          and tapers it with a cosine taper NT seconds long from 
%          begin point T1-NT and with reverse cosine taper from 
%          point T2 to point T2+NT. Points outside the range 
%          (T1-NT,T2+NT) are zeroed. If T1/T2 is negative then
%          taper is not implemented at beginning/end. If X is an
%          array of seismograms, then the taper is applied to each
%          row of X.
%
nx=max(size(x));
ns=min(size(x));
taper=ones(1,nx);
it=[0:fix(nt/dt)]*dt/nt;
ct=0.5-0.5*cos(pi*it);
it1=fix(t1/dt+1);
it2=fix(t2/dt+1);
if t1 > 0
  taper(it1-fix(nt/dt):it1)=ct;
  taper(1:it1-fix(nt/dt))=zeros(size(1:it1-fix(nt/dt)));
end
if t2 > 0
  if t2 > nx*dt-nt
     [t2,nx*dt]
     error ('T2 > NX * DT - NT')
  end
  taper(it2:it2+fix(nt/dt))=fliplr(ct);
  taper(it2+fix(nt/dt):nx)=zeros(size(taper(it2+fix(nt/dt):nx)));
end
for is=1:ns
  y(is,:)=taper.*x(is,:);
end