  A quantum phase transition is typically induced by tuning an external
parameter that appears as a coupling constant in the Hamiltonian. Another route
is to vary the global symmetry of the system, generalizing, e.g., SU(2) to
SU(N). In that case, however, the discrete nature of the control parameter
prevents one from identifying and characterizing the transition. We show how
this limitation can be overcome for the SU(N) Heisenberg model with the help of
a singlet projector algorithm that can treat N continuously. On the square
lattice, we find a direct, continuous phase transition between Neel-ordered and
crystalline bond-ordered phases at Nc=4.57(5) with critical exponents z=1 and
beta/nu=0.81(3).
