function w=cleanmatrix(mat, scale)
% usage: w=cleanmatrix(mat,scale)
% dscription: zeros out entries <scale*||mat||_inf.
% Argument scale is optional, default is eps.

if (nargin == 1)
  scale = eps;
end
xmat = scale*norm(mat,inf);
w = (abs(mat) > xmat) .* mat;