function current = bslowf
% bslowf Replaces low value with midpoint, returns new midpoint [PHYS210-bs]
   global Bs_low Bs_high Bs_tol Bs_progress;
   if ~ bsinitialized
      warning('Search not initialized.  Use bsnew(low, high).');
      return;
   end
   Bs_low(end+1) = bscurrent;
   Bs_progress(end+1) = 0;
   current = bscurrent;
end
