Current methods for gravity smoothing in SPH simulations of star formation smooth the gravitational force using the SPH kernel. The smoothing length may be determined from the density, or from the rule that a fixed number of neighbours must interact. However, this smoothing is not consistent with the equations of motion. In this talk I will discuss how the smoothing can be made consistent by starting with a Lagrangian for the system. The result is that there is an extra force associated with the smoothing. Simulations of a disk system illustrate how this effects the fragmentation of the disk.
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