function uout=thumbfin(u,umin,umax,goplot);
%function uout=thumbfin(u,umin,umax,goplot);
%            thumbfinger filter
g=find(u(:)~=nan);
bad=find( (u(g)<umin)|(u(g)>umax) );
uout=u;
if length(bad)>0
       uout(g(bad))=ones(1,length(bad))*NaN;
end
if (nargin>3)&(length(bad)>0)
      plot(g,u(g),g(bad),u(g(bad)),'x')
end
