adding back files to be reviewed

include/openmc/distribution_multi.h

@@ -0,0 +1,80 @@
+#ifndef DISTRIBUTION_MULTI_H
+#define DISTRIBUTION_MULTI_H
+
+#include <memory>
+
+#include "pugixml.hpp"
+
+#include "openmc/distribution.h"
+#include "openmc/position.h"
+
+namespace openmc {
+
+//==============================================================================
+//! Probability density function for points on the unit sphere. Extensions of
+//! this type are used to sample angular distributions for starting sources
+//==============================================================================
+
+class UnitSphereDistribution {
+public:
+  UnitSphereDistribution() { };
+  explicit UnitSphereDistribution(Direction u) : u_ref_{u} { };
+  explicit UnitSphereDistribution(pugi::xml_node node);
+  virtual ~UnitSphereDistribution() = default;
+
+  //! Sample a direction from the distribution
+  //! \return Direction sampled
+  virtual Direction sample() const = 0;
+
+  Direction u_ref_ {0.0, 0.0, 1.0};  //!< reference direction
+};
+
+//==============================================================================
+//! Explicit distribution of polar and azimuthal angles
+//==============================================================================
+
+class PolarAzimuthal : public UnitSphereDistribution {
+public:
+  PolarAzimuthal(Direction u, UPtrDist mu, UPtrDist phi);
+  explicit PolarAzimuthal(pugi::xml_node node);
+
+  //! Sample a direction from the distribution
+  //! \return Direction sampled
+  Direction sample() const;
+private:
+  UPtrDist mu_;  //!< Distribution of polar angle
+  UPtrDist phi_; //!< Distribution of azimuthal angle
+};
+
+//==============================================================================
+//! Uniform distribution on the unit sphere
+//==============================================================================
+
+class Isotropic : public UnitSphereDistribution {
+public:
+  Isotropic() { };
+
+  //! Sample a direction from the distribution
+  //! \return Sampled direction
+  Direction sample() const;
+};
+
+//==============================================================================
+//! Monodirectional distribution
+//==============================================================================
+
+class Monodirectional : public UnitSphereDistribution {
+public:
+  Monodirectional(Direction u) : UnitSphereDistribution{u} { };
+  explicit Monodirectional(pugi::xml_node node) : UnitSphereDistribution{node} { };
+
+  //! Sample a direction from the distribution
+  //! \return Sampled direction
+  Direction sample() const;
+};
+
+using UPtrAngle = std::unique_ptr<UnitSphereDistribution>;
+
+} // namespace openmc
+
+#endif // DISTRIBUTION_MULTI_H