  Generating a text abstract from a set of documents remains a challenging
task. The neural encoder-decoder framework has recently been exploited to
summarize single documents, but its success can in part be attributed to the
availability of large parallel data automatically acquired from the Web. In
contrast, parallel data for multi-document summarization are scarce and costly
to obtain. There is a pressing need to adapt an encoder-decoder model trained
on single-document summarization data to work with multiple-document input. In
this paper, we present an initial investigation into a novel adaptation method.
It exploits the maximal marginal relevance method to select representative
sentences from multi-document input, and leverages an abstractive
encoder-decoder model to fuse disparate sentences to an abstractive summary.
The adaptation method is robust and itself requires no training data. Our
system compares favorably to state-of-the-art extractive and abstractive
approaches judged by automatic metrics and human assessors.
