function nu=normal2d(v)
% nu=normal2d(v)
% compute outside normal togiven a tangent vector v 
%  in counterclockwise direction
% 
%   /////////////
%   -------------> v
%        |
%        |  n
%        |
%        v
%

nu = [v(2),-v(1)]/norm(v);
nu =reshape(nu,size(v));