1. A method comprising: identifying multiple subspaces of a set of input vectors of a design; running a numerical solver on the multiple subspaces previously identified, the numerical solver determining if any solution to a set of input constraints exists in the multiple subspaces; and searching, in hierarchical stages, the multiple subspaces for unique input vectors that satisfy the set of input constraints, the searching using a different seed for each of the hierarchical stages, and the searching excluding at least a portion of at least one of the multiple subspaces based upon the numerical solver determining that no solution to the set of input constraints exists in the at least one of the multiple subspaces.