diff options
| -rw-r--r-- | src/photon.h | 60 | ||||
| -rw-r--r-- | tests/rayleigh.py | 56 |
2 files changed, 97 insertions, 19 deletions
diff --git a/src/photon.h b/src/photon.h index 45ad79b..e781864 100644 --- a/src/photon.h +++ b/src/photon.h @@ -105,30 +105,52 @@ __device__ void fill_state(State &s, Photon &p) } // fill_state -__device__ void rayleigh_scatter(Photon &p, curandState &rng) +__device__ float3 pick_new_direction(float3 axis, float theta, float phi) { - float theta, y; - - while (true) - { - y = curand_uniform(&rng); - theta = uniform(&rng, 0, 2*PI); - - if (y < powf(cosf(theta),2)) - break; + // Taken from SNOMAN rayscatter.for + float cos_theta = cosf(theta); + float sin_theta = sinf(theta); + float cos_phi = cosf(phi); + float sin_phi = sinf(phi); + + float sin_axis_theta = sqrt(1.0f - axis.z*axis.z); + float cos_axis_phi, sin_axis_phi; + + if (isnan(sin_axis_theta) || sin_axis_theta < 0.00001f) { + cos_axis_phi = 1.0f; + sin_axis_phi = 0.0f; + } else { + cos_axis_phi = axis.x / sin_axis_theta; + sin_axis_phi = axis.y / sin_axis_theta; } - float phi = uniform(&rng, 0, 2*PI); - - float3 b = cross(p.polarization, p.direction); - float3 c = p.polarization; - - p.direction = rotate(p.direction, theta, b); - p.direction = rotate(p.direction, phi, c); + return make_float3(cos_theta*axis.x + sin_theta*(axis.z*cos_phi*cos_axis_phi - sin_phi*sin_axis_phi), + cos_theta*axis.y + sin_theta*(cos_phi*axis.z*sin_axis_phi - sin_phi*cos_axis_phi), + cos_theta*axis.z - sin_theta*cos_phi*sin_axis_theta); +} - p.polarization = rotate(p.polarization, theta, b); - p.polarization = rotate(p.polarization, phi, c); +__device__ void rayleigh_scatter(Photon &p, curandState &rng) +{ + float cos_theta = 2.0f*cosf((acosf(1.0f - 2.0f*curand_uniform(&rng))-2*PI)/3.0f); + if (cos_theta > 1.0f) + cos_theta = 1.0f; + else if (cos_theta < -1.0f) + cos_theta = -1.0f; + + float theta = acosf(cos_theta); + float phi = uniform(&rng, 0.0f, 2.0f * PI); + + p.direction = pick_new_direction(p.polarization, theta, phi); + + if (1.0f - fabsf(cos_theta) < 1e-6f) { + p.polarization = pick_new_direction(p.polarization, PI/2.0f, phi); + } else { + // linear combination of old polarization and new direction + p.polarization = p.polarization - cos_theta * p.direction; + } + p.direction /= norm(p.direction); + p.polarization /= norm(p.polarization); } // scatter __device__ int propagate_to_boundary(Photon &p, State &s, curandState &rng) diff --git a/tests/rayleigh.py b/tests/rayleigh.py new file mode 100644 index 0000000..4394ada --- /dev/null +++ b/tests/rayleigh.py @@ -0,0 +1,56 @@ +import unittest +import numpy as np + +from chroma.geometry import Solid, Geometry +from chroma.make import box +from chroma.sim import Simulation +from chroma.optics import water_wcsim +from chroma.event import Photons +import histogram +from histogram.root import rootify +import ROOT +ROOT.gROOT.SetBatch(1) + +class TestRayleigh(unittest.TestCase): + def setUp(self): + self.cube = Geometry() + self.cube.add_solid(Solid(box(100,100,100), water_wcsim, water_wcsim)) + self.cube.pmtids = [0] + self.sim = Simulation(self.cube, water_wcsim, bvh_bits=4, geant4_processes=0, + use_cache=False) + nphotons = 100000 + positions = np.tile([0,0,0], (nphotons,1)).astype(np.float32) + directions = np.tile([0,0,1], (nphotons,1)).astype(np.float32) + polarizations = np.zeros_like(positions) + phi = np.random.uniform(0, 2*np.pi, nphotons).astype(np.float32) + polarizations[:,0] = np.cos(phi) + polarizations[:,1] = np.sin(phi) + times = np.zeros(nphotons, dtype=np.float32) + wavelengths = np.empty(nphotons, np.float32) + wavelengths.fill(400.0) + + self.photons = Photons(positions=positions, directions=directions, polarizations=polarizations, + times=times, wavelengths=wavelengths) + + def testAngularDistributionPolarized(self): + # Fully polarized photons + self.photons.polarizations[:] = [1.0, 0.0, 0.0] + + photon_stop = self.sim.propagate_photons(self.photons, max_steps=1) + aborted = (photon_stop.histories & (1 << 31)) > 0 + self.assertFalse(aborted.any()) + + # Compute the dot product between initial and final directions + rayleigh_scatters = (photon_stop.histories & (1 << 4)) > 0 + cos_scatter = (self.photons.directions[rayleigh_scatters] * photon_stop.directions[rayleigh_scatters]).sum(axis=1) + theta_scatter = np.arccos(cos_scatter) + h = histogram.Histogram(bins=100, range=(0, np.pi)) + h.fill(theta_scatter) + h = rootify(h) + + # The functional form for polarized light should be (1 + \cos^2 \theta)\sin \theta + # according to GEANT4 physics reference manual + f = ROOT.TF1("pol_func", "[0]*(1+cos(x)**2)*sin(x)", 0, np.pi) + h.Fit(f) + self.assertGreater(f.GetProb(), 1e-3) + |