lowerRankLociA(d1',relPfaf)lowerRankLociA(d1',relPfaf,Sa)The quadratic (Pfaffian) relations define a complete intersection variety $Q$ in a $\mathbb{P}^n$ of $a$-variables. In this procedure, we compute the loci of points in $Q$ at which the rank of $a$-matrix drops, that is, the minimal primes of the maximal minors of the $a$-matrix (within the variety $Q$). These loci play an important role for the construction of numerical Godeaux surfaces with hyperelliptic fibers.
The object lowerRankLociA is a method function.