Error halts simulation

[griff10000]

Simulation halts prematurely with following error: C:\Users\Graham\anaconda3\lib\site-packages\matplotlib\animation.py:889: UserWarning: Animation was deleted without rendering anything. This is most likely not intended. To prevent deletion, assign the Animation to a variable, e.g. anim, that exists until you have outputted the Animation using plt.show()oranim.save().

The recommended action seems to have been included in the code so not sure how to proceed.