@article{10_1017_S0017089500003062,
     author = {Waller, Derek A.},
     title = {Optimisation of quadratic forms associated with graphs},
     journal = {Glasgow mathematical journal},
     pages = {79--85},
     year = {1977},
     volume = {18},
     number = {1},
     doi = {10.1017/S0017089500003062},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0017089500003062/}
}