function [s] = ricker(npts,freq,dt,timesh,nsw)
%  Calculates Ricker wavelet
%  s(npts) = wavelet
%  dt = sampling interval
%  freq = predominate frequency of wavelet
%  timesh = time shift to the left (s)
%  nsw = number of points on each side of wavelet to be tapered 
%        by half of a cosine bell window
if timesh<.0001; timesh=npts*dt/2; end
pi2 = sqrt(pi)/2;
b = sqrt(6)/(pi*freq);
const = 2*sqrt(6)/b;
for i = 1:npts
   tim1 = (i-1)*dt;
   tim2 = tim1 - timesh;
   u = const*tim2;
   amp = ((u*u)/4 - 0.5)*pi2*(exp(-u*u/4));
   s(i) = amp;
end

smax = max(abs(s));
smax=smax*2;
s = s/smax;
if nsw~=0
   for i = 1:nsw
      j = nsw-i;
      fac = 0.5*(cos(pi*j/nsw) + 1);
      s(i) = s(i)*fac;
   end
   for i = 1:nsw
      j = i-1;
      fac = 0.5*(cos(pi*j/nsw) + 1);
      k = npts-nsw+i;
      s(k) = s(k)*fac;
   end
end