diff --git a/jaxpm/kernels.py b/jaxpm/kernels.py index c3306c6..97d34dd 100644 --- a/jaxpm/kernels.py +++ b/jaxpm/kernels.py @@ -98,3 +98,29 @@ def cic_compensation(kvec): kwts = [np.sinc(kvec[i] / (2 * np.pi)) for i in range(3)] wts = (kwts[0] * kwts[1] * kwts[2])**(-2) return wts + +def PGD_kernel(kvec, kl, ks): + """ + Computes the PGD kernel + Parameters: + ----------- + kvec: array + Array of k values in Fourier space + kl: float + initial long range scale parameter + ks: float + initial dhort range scale parameter + Returns: + -------- + v: array + kernel + """ + kk = sum(ki**2 for ki in kvec) + kl2 = kl**2 + ks4 = ks**4 + mask = (kk == 0).nonzero() + kk[mask] = 1 + v = jnp.exp(-kl2 / kk) * jnp.exp(-kk**2 / ks4) + imask = (~(kk == 0)).astype(int) + v *= imask + return v \ No newline at end of file diff --git a/jaxpm/pm.py b/jaxpm/pm.py index 3f39c9c..d9870f7 100644 --- a/jaxpm/pm.py +++ b/jaxpm/pm.py @@ -3,7 +3,7 @@ import jax_cosmo as jc -from jaxpm.kernels import fftk, gradient_kernel, laplace_kernel, longrange_kernel +from jaxpm.kernels import fftk, gradient_kernel, laplace_kernel, longrange_kernel, PGD_kernel from jaxpm.painting import cic_paint, cic_read from jaxpm.growth import growth_factor, growth_rate, dGfa @@ -70,3 +70,27 @@ def nbody_ode(state, a, cosmo): return dpos, dvel return nbody_ode + + +def pgd_correction(pos, params): + """ + improve the short-range interactions of PM-Nbody simulations with potential gradient descent method, based on https://arxiv.org/abs/1804.00671 + args: + pos: particle positions [npart, 3] + params: [alpha, kl, ks] pgd parameters + """ + kvec = fftk(mesh_shape) + + delta = cic_paint(jnp.zeros(mesh_shape), pos) + alpha, kl, ks = params + delta_k = jnp.fft.rfftn(delta) + PGD_range=PGD_kernel(kvec, kl, ks) + + pot_k_pgd=(delta_k * laplace_kernel(kvec))*PGD_range + + forces_pgd= jnp.stack([cic_read(jnp.fft.irfftn(gradient_kernel(kvec, i)*pot_k_pgd), pos) + for i in range(3)],axis=-1) + + dpos_pgd = forces_pgd*alpha + + return dpos_pgd \ No newline at end of file