After having 是什么用法?

问题描述:

After having 是什么用法?
After having decided to take some presents to a children's hospital,the circus owner,……………………
这句话开头的After having是什么用法?怎么having后还跟过去式?什么时态啊?

after是介词,后跟ing形式
having decided to是非谓语动词 动名词的完成时