function rotMatrix = rot(axis,angle)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% return a rotation matrix from a rotation around axis about angle
% axis: 1-x,2-y,3-z
% angle:
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
switch axis
    case 1
        rotMatrix = [1    0        0;
                     0  cos(angle) -sin(angle);
                     0  sin(angle) cos(angle)];
    case 2
        rotMatrix = [cos(angle)    0        sin(angle);
                     0             1        0;
                    -sin(angle)    0        cos(angle)];
    case 3
        rotMatrix = [cos(angle) -sin(angle)  0;
                     sin(angle) cos(angle)   0;
                     0           0           1];
    otherwise
        rotMatrix = eye(3);
end