There's four papers linked in the article. The last three (see below) were pretty good, haven't read the first. http://arxiv.org/pdf/1412.0035v1.pdf http://arx

There's four papers linked in the article. The last three (see below) were pretty good, haven't read the first. http://arxiv.org/pdf/1412.0035v1.pdf http://arxiv.org/pdf/1412.0035v1.pdf http://arxiv.org/pdf/1506.02753.pdf http://arxiv.org/pdf/1506.02753.pdf http://arxiv.org/pdf/1312.6034v2.pdf http://arxiv.org/pdf/1312.6034v2.pdf