Neil Gaiman

Purpose/Main point
His purpose was to encourage the graduates to make good art.
His main point was that life can be tough, but you must keep going.

Dramatistic Pentad
The purpose was too encourage the graduates to make good art.
The act was addressing the graduates.  
The scene was the graduation ceremony for the University of the Arts.
For agency, Gaiman simply stood and spoke to the graduating class. 
The agent was Neil Gaiman, a renowned writer.

Significant ratios
Agent/Purpose - As a renowned writer himself, he was able to speak from personal experience.  
Agent/Scene - As a renowned writer, he had already done what he was inspiring them to do...giving him credibility and making it believable that they could actually do what he said they could do.