Construction of systems of differential equations of Okubo normal form with rigid monodromy

For systems of differential equations of the form (xI _n – T )dy /dx = Ay (systems of Okubo normal form), where A is an n × n constant matrix and T is an n × n constant diagonal matrix, two kinds of operations (extension and restriction) are defined. It is shown that every irreducible system of Okubo normal form of semi‐simple type whose monodromy representation is rigid is obtained from a rank 1 system of Okubo normal form by a finite iteration of the operations. Moreover, an algorithm to calculate the generators of monodromy groups for rigid systems of Okubo normal form is given. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)