Implement angular PDF evaluation for angle-energy distributions

include/openmc/angle_energy.h

@@ -14,8 +14,22 @@ namespace openmc {
 
 class AngleEnergy {
 public:
+  //! Sample an outgoing energy and scattering cosine
+  //! \param[in] E_in Incoming energy in [eV]
+  //! \param[out] E_out Outgoing energy in [eV]
+  //! \param[out] mu Outgoing cosine with respect to current direction
+  //! \param[inout] seed Pseudorandom seed pointer
   virtual void sample(
     double E_in, double& E_out, double& mu, uint64_t* seed) const = 0;
+
+  //! Sample an outgoing energy and evaluate the angular PDF
+  //! \param[in] E_in Incoming energy in [eV]
+  //! \param[in] mu Scattering cosine with respect to current direction
+  //! \param[out] E_out Outgoing energy in [eV]
+  //! \param[inout] seed Pseudorandom seed pointer
+  //! \return Probability density for the scattering cosine
+  virtual double sample_energy_and_pdf(
+    double E_in, double mu, double& E_out, uint64_t* seed) const = 0;
   virtual ~AngleEnergy() = default;
 };
 

include/openmc/chain.h

@@ -71,6 +71,15 @@ class DecayPhotonAngleEnergy : public AngleEnergy {
   void sample(
     double E_in, double& E_out, double& mu, uint64_t* seed) const override;
 
+  //! Sample an outgoing energy and evaluate the angular PDF
+  //! \param[in] E_in Incoming energy in [eV]
+  //! \param[in] mu Scattering cosine with respect to current direction
+  //! \param[out] E_out Outgoing energy in [eV]
+  //! \param[inout] seed Pseudorandom seed pointer
+  //! \return Probability density for the scattering cosine
+  double sample_energy_and_pdf(
+    double E_in, double mu, double& E_out, uint64_t* seed) const override;
+
 private:
   const Distribution* photon_energy_;
 };

include/openmc/distribution_angle.h

@@ -26,6 +26,12 @@ class AngleDistribution {
   //! \return Cosine of the angle in the range [-1,1]
   double sample(double E, uint64_t* seed) const;
 
+  //! Evaluate the angular PDF at a given energy and cosine
+  //! \param[in] E Particle energy in [eV]
+  //! \param[in] mu Cosine of the scattering angle
+  //! \return Probability density for the scattering cosine
+  double evaluate(double E, double mu) const;
+
   //! Determine whether angle distribution is empty
   //! \return Whether distribution is empty
   bool empty() const { return energy_.empty(); }

include/openmc/distribution_multi.h

@@ -6,6 +6,7 @@
 #include "pugixml.hpp"
 
 #include "openmc/distribution.h"
+#include "openmc/error.h"
 #include "openmc/position.h"
 
 namespace openmc {
@@ -29,6 +30,14 @@ class UnitSphereDistribution {
   //! \return (sampled Direction, sample weight)
   virtual std::pair<Direction, double> sample(uint64_t* seed) const = 0;
 
+  //! Evaluate the probability density for a given direction
+  //! \param[in] u Direction on the unit sphere
+  //! \return Probability density at the given direction
+  virtual double evaluate(Direction u) const
+  {
+    fatal_error("evaluate not available for this UnitSphereDistribution type");
+  }
+
   Direction u_ref_ {0.0, 0.0, 1.0}; //!< reference direction
 };
 
@@ -52,6 +61,11 @@ class PolarAzimuthal : public UnitSphereDistribution {
   //! \return (sampled Direction, value of the PDF at this Direction)
   std::pair<Direction, double> sample_as_bias(uint64_t* seed) const;
 
+  //! Evaluate the probability density for a given direction
+  //! \param[in] u Direction on the unit sphere
+  //! \return Probability density at the given direction
+  double evaluate(Direction u) const override;
+
   // Observing pointers
   Distribution* mu() const { return mu_.get(); }
   Distribution* phi() const { return phi_.get(); }
@@ -87,6 +101,11 @@ class Isotropic : public UnitSphereDistribution {
   //! \return (sampled direction, sample weight)
   std::pair<Direction, double> sample(uint64_t* seed) const override;
 
+  //! Evaluate the probability density for a given direction
+  //! \param[in] u Direction on the unit sphere
+  //! \return Probability density at the given direction
+  double evaluate(Direction u) const override;
+
   // Set or get bias distribution
   void set_bias(std::unique_ptr<PolarAzimuthal> bias)
   {

include/openmc/reaction_product.h

@@ -49,6 +49,21 @@ class ReactionProduct {
   //! \param[inout] seed Pseudorandom seed pointer
   void sample(double E_in, double& E_out, double& mu, uint64_t* seed) const;
 
+  //! Select which angle-energy distribution to sample
+  //! \param[in] E_in Incoming energy in [eV]
+  //! \param[inout] seed Pseudorandom seed pointer
+  //! \return Reference to the selected angle-energy distribution
+  AngleEnergy& sample_dist(double E_in, uint64_t* seed) const;
+
+  //! Sample an outgoing energy and evaluate the angular PDF
+  //! \param[in] E_in Incoming energy in [eV]
+  //! \param[in] mu Scattering cosine with respect to current direction
+  //! \param[out] E_out Outgoing energy in [eV]
+  //! \param[inout] seed Pseudorandom seed pointer
+  //! \return Probability density for the scattering cosine
+  double sample_energy_and_pdf(
+    double E_in, double mu, double& E_out, uint64_t* seed) const;
+
   ParticleType particle_;      //!< Particle type
   EmissionMode emission_mode_; //!< Emission mode
   double decay_rate_; //!< Decay rate (for delayed neutron precursors) in [1/s]

include/openmc/secondary_correlated.h

@@ -41,6 +41,22 @@ class CorrelatedAngleEnergy : public AngleEnergy {
   void sample(
     double E_in, double& E_out, double& mu, uint64_t* seed) const override;
 
+  //! Sample the outgoing energy and return the angular distribution
+  //! \param[in] E_in Incoming energy in [eV]
+  //! \param[out] E_out Outgoing energy in [eV]
+  //! \param[inout] seed Pseudorandom seed pointer
+  //! \return Reference to the angular distribution at the sampled energy bin
+  Distribution& sample_dist(double E_in, double& E_out, uint64_t* seed) const;
+
+  //! Sample an outgoing energy and evaluate the angular PDF
+  //! \param[in] E_in Incoming energy in [eV]
+  //! \param[in] mu Scattering cosine with respect to current direction
+  //! \param[out] E_out Outgoing energy in [eV]
+  //! \param[inout] seed Pseudorandom seed pointer
+  //! \return Probability density for the scattering cosine
+  double sample_energy_and_pdf(
+    double E_in, double mu, double& E_out, uint64_t* seed) const override;
+
   // energy property
   vector<double>& energy() { return energy_; }
   const vector<double>& energy() const { return energy_; }

include/openmc/secondary_kalbach.h

@@ -32,6 +32,24 @@ class KalbachMann : public AngleEnergy {
   void sample(
     double E_in, double& E_out, double& mu, uint64_t* seed) const override;
 
+  //! Sample outgoing energy and Kalbach-Mann parameters
+  //! \param[in] E_in Incoming energy in [eV]
+  //! \param[out] E_out Outgoing energy in [eV]
+  //! \param[out] km_a Kalbach-Mann 'a' parameter
+  //! \param[out] km_r Kalbach-Mann pre-compound fraction 'r'
+  //! \param[inout] seed Pseudorandom seed pointer
+  void sample_params(double E_in, double& E_out, double& km_a, double& km_r,
+    uint64_t* seed) const;
+
+  //! Sample an outgoing energy and evaluate the angular PDF
+  //! \param[in] E_in Incoming energy in [eV]
+  //! \param[in] mu Scattering cosine with respect to current direction
+  //! \param[out] E_out Outgoing energy in [eV]
+  //! \param[inout] seed Pseudorandom seed pointer
+  //! \return Probability density for the scattering cosine
+  double sample_energy_and_pdf(
+    double E_in, double mu, double& E_out, uint64_t* seed) const override;
+
 private:
   //! Outgoing energy/angle at a single incoming energy
   struct KMTable {

include/openmc/secondary_nbody.h

@@ -28,6 +28,21 @@ class NBodyPhaseSpace : public AngleEnergy {
   void sample(
     double E_in, double& E_out, double& mu, uint64_t* seed) const override;
 
+  //! Sample an outgoing energy from the N-body phase space distribution
+  //! \param[in] E_in Incoming energy in [eV]
+  //! \param[inout] seed Pseudorandom seed pointer
+  //! \return Sampled outgoing energy in [eV]
+  double sample_energy(double E_in, uint64_t* seed) const;
+
+  //! Sample an outgoing energy and evaluate the angular PDF
+  //! \param[in] E_in Incoming energy in [eV]
+  //! \param[in] mu Scattering cosine with respect to current direction
+  //! \param[out] E_out Outgoing energy in [eV]
+  //! \param[inout] seed Pseudorandom seed pointer
+  //! \return Probability density for the scattering cosine
+  double sample_energy_and_pdf(
+    double E_in, double mu, double& E_out, uint64_t* seed) const override;
+
 private:
   int n_bodies_;      //!< Number of particles distributed
   double mass_ratio_; //!< Total mass of particles [neutron mass]