Even when its origins are still uncertain, the uses of calendula as a medicine and as a colouring were known to the old herbalists, especially Arabs and Hindus. Greeks, who started cultivating it more recently, used calendula flowers to decorate their feasts and to make garlands to honour their heroes....

Most physical plants are nonlinear in nature and coupled with uncertain dynamics due to external disturbances or unmodeled nonlinearities or even unpredictable faults....