Above image shows again the topology of the Jacobian of
the velocity field visualized in the
previous image.
Points in the flow with a zero velocity are called
critical points.
In the above picture they are
shown as sets of arrows and disks. The arrows point in the
direction of the real eigenvectors with length proportional
to the scaled eigenvalue and color denoting the sign of the
eigenvalue.
The disks are in the plane spanned by the complex eigenvectors,
with color and diameter of a disk proportional to sign and
absolute value, respectively, of the real and imaginary part of an
eigenvalue.
Note that the Jacobian is an unsymmetric second-order tensor and that
therefore these glyphs are suitabel for a general second-order tensor.