  We develop a multiscale hybrid scheme for simulations of soft condensed
matter systems, which allows one to treat the system at the particle level in
selected regions of space, and at the continuum level elsewhere. It is derived
systematically from an underlying particle-based model by field theoretic
methods. Particles in different representation regions can switch
representations on the fly, controlled by a spatially varying tuning function.
As a test case, the hybrid scheme is applied to simulate colloid-polymer
composites with high resolution regions close to the colloids. The hybrid
simulations are significantly faster than reference simulations of a pure
particle-based model, and the results are in good agreement.
