  There are efficient many-body methods, such as the (symmetry-restored)
generator coordinate method in nuclear physics, that formulate the A-body
Schr\"odinger equation within a set of nonorthogonal many-body states. Solving
the corresponding secular equation requires the evaluation of the norm matrix
and thus the capacity to compute its entries consistently and without any phase
ambiguity. This is not always a trivial task, e.g. it remained a long-standing
problem for methods based on general Bogoliubov product states. While a
solution to this problem was found recently in Ref. [L. M. Robledo, Phys. Rev.
C79, 021302 (2009)], the present work introduces an alternative method that can
be generically applied to other classes of states of interest in many-body
physics. The method is presently exemplified in the case of Bogoliubov states
and numerically illustrated on the basis of a toy model.
