Pinched hysteresis loops and symmetry
Pinched hysteresis loops (PHLs) can be clockwise, counter-clockwise, self-crossing and non-self-crossing. While it is difficult to differentiate these features from the measured PHLs on the oscilloscope, this study shows that PHL exhibits different forms of symmetry. Self-crossing PHLs display reflection symmetry and non-self-crossing ones display point symmetry. These features are confirmed with practical measurements based on the memristor characteristics of Hewlett-Packard (self-crossing) and of a discharge lamp (non-self-crossing). It is shown that the symmetry graph is a useful tool to identify the features of PHLs.