T - IfB

Particle – Mesh algorithm• Nearest Grid Point“ (NGP): Put particle on nearestgrid point and also evaluate its force at the nearestgrid point.• „Cloud In Cell“ (CIC): Assign the charge to the 2 dnearest grid points and also interpolate fromthese 2 d grid points.Method goes like O(N lnN) because of FFT.„Computer Simulations using Particles“ by R.W. Hockneyand J.W. Eastwood (McGraw-Hill, New York, 1981)103Particle – Mesh algorithmd( r ) ( r ') g( r r ') d r 'Green‘s function for 3d gravity: gr ( ) Gr ( k) ( k) g( k)Fourier transformation:with Ggk ( ) 2kor better (differentiable at k = π/L): gk ( ) 1kL kL kL2 2 2sin / 2 sin / 2 sin / 2x y z104