This note extends the algorithm of [hess] for computing unimodular Galois groups of irreducible differential equations of order four. The main tool is invariant theory.
@article{bwmeta1.element.bwnjournal-article-doi-10_4064-bc58-0-7,
author = {Julia Hartmann},
title = {Invariants and differential Galois groups in degree four},
journal = {Banach Center Publications},
volume = {58},
year = {2002},
pages = {79-87},
zbl = {1030.12003},
language = {en},
url = {http://dml.mathdoc.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-bc58-0-7}
}
Julia Hartmann. Invariants and differential Galois groups in degree four. Banach Center Publications, Tome 58 (2002) pp. 79-87. http://gdmltest.u-ga.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-bc58-0-7/