% convection-diffusion
% (\grad u \cdot b) v 
% Definition of the vector field 'b'
% Coord(nip,2)

function b = b_vecV(Coord,flag,tita)

[n,m]=size(Coord);
b = zeros(n,m);

if flag==0,
   return
end

if flag==1,
   b(:,1) = (1-cos(Coord(:,1)*tita))*cos(tita); 
   b(:,2) = (1-sin(Coord(:,2)*tita))*sin(tita); 
   return, 
end
if flag==2,
   b(:,1) = tita*(1+Coord(:,1).^3); 
   b(:,2) = Coord(:,2).^3; 
   return, 
end
if flag==3,
   b(:,1) = -ones(n,1); 
   b(:,2) = zeros(n,1); 
   return, 
end
if flag==4,
   b=ones(n,m); 
   return, 
end
if flag==5,
   b(:,1) = atan(20*Coord(:,1)-20);
   b(:,2) = ones(n,1); 
   return, 
end

%disp('b_vec: Wrong flag. Zero convection assumed.')

return