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The spurious pressure jump at a contact discontinuity, in SPH simulations ofthe compressible Euler equations is investigated. From the spatiotemporalbehaviour of the error, the SPH pressure jump is likened to entropy errorsobserved for artificial viscosity based finite difference/volume schemes. Theerror is observed to be generated at start-up and dissipation is the onlyrecourse to mitigate it's effect. We show that similar errors are generated forthe Lagrangian plus remap version of the Piecewise Parabolic Method (PPM)finite volume code (PPMLR). Through a comparison with the direct Eulerianversion of the PPM code (PPMDE), we argue that a lack of diffusion across thematerial wave (contact discontinuity) is responsible for the error in PPMLR. Weverify this hypothesis by constructing a more dissipative version of the remapcode using a piecewise constant reconstruction. As an application to SPH, wepropose a hybrid GSPH scheme that adds the requisite dissipation by utilizing amore dissipative Riemann solver for the energy equation. The proposedmodification to the GSPH scheme, and it's improved treatment of the anomaly isverified for flows with strong shocks in one and two dimensions. The resultthat dissipation must act across the density and energy equations provides aconsistent explanation for many of the hitherto proposed "cures" or "fixes" forthe problem.

SPH Entropy Errors and the Pressure Blip