  In this paper a simple, robust, and general purpose approach to implement the
Incompressible Smoothed Particle Hydrodynamics (ISPH) method is proposed. This
approach is well suited for implementation on CPUs and GPUs. The method is
matrix-free and uses an iterative formulation to setup and solve the
pressure-Poisson equation. A novel approach is used to ensure homogeneous
particle distributions and improved boundary conditions. This formulation
enables the use of solid wall boundary conditions from the weakly-compressible
SPH schemes. The method is fast and runs on GPUs without the need for complex
integration with sparse linear solvers. We show that this approach is
sufficiently accurate and yet efficient compared to other approaches. Several
benchmark problems that illustrate the robustness, performance, and wide range
of applicability of the new scheme are demonstrated. An open source
implementation is provided and the manuscript is fully reproducible.
