@article{DIMsets,
    author = {P. Fr\"anti and O. Virmajoki and V. Hautam\"aki},
    title = {Fast agglomerative clustering using a k-nearest neighbor graph},
    journal = {IEEE Trans. on Pattern Analysis and Machine Intelligence},
    year = {2006},
    volume = {28},
    number = {11},
    pages = {1875--1881}
}