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Source biasing capabilities (#3460)
Co-authored-by: Paul Romano <paul.k.romano@gmail.com>
This commit is contained in:
Jack Fletcher
GitHub
parent
37e2feb34b
commit
0486e433d2
24 changed files with 2003 additions and 252 deletions
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@ -15,6 +15,17 @@
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namespace openmc {
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//==============================================================================
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// Helper function for computing importance weights from biased sampling
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//==============================================================================
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//! Compute importance weights for biased sampling
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//! \param p Unnormalized original probability vector
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//! \param b Unnormalized bias probability vector
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//! \return Vector of importance weights (p_norm[i] / b_norm[i])
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vector<double> compute_importance_weights(
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const vector<double>& p, const vector<double>& b);
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//==============================================================================
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//! Abstract class representing a univariate probability distribution
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//==============================================================================
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@ -22,11 +33,41 @@ namespace openmc {
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class Distribution {
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public:
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virtual ~Distribution() = default;
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virtual double sample(uint64_t* seed) const = 0;
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//! Sample a value from the distribution, handling biasing automatically
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//! \param seed Pseudorandom number seed pointer
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//! \return (sampled value, importance weight)
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virtual std::pair<double, double> sample(uint64_t* seed) const;
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//! Evaluate probability density, f(x), at a point
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//! \param x Point to evaluate f(x)
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//! \return f(x)
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virtual double evaluate(double x) const;
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//! Return integral of distribution
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//! \return Integral of distribution
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virtual double integral() const { return 1.0; };
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//! Set bias distribution
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virtual void set_bias(std::unique_ptr<Distribution> bias)
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{
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bias_ = std::move(bias);
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}
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const Distribution* bias() const { return bias_.get(); }
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protected:
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//! Sample a value (unbiased) from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled value
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virtual double sample_unbiased(uint64_t* seed) const = 0;
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//! Read bias distribution from XML
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//! \param node XML node that may contain a bias child element
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void read_bias_from_xml(pugi::xml_node node);
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// Biasing distribution
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unique_ptr<Distribution> bias_;
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};
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using UPtrDist = unique_ptr<Distribution>;
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@ -50,7 +91,7 @@ public:
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//! Sample a value from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled value
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//! \return Sampled index
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size_t sample(uint64_t* seed) const;
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// Properties
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@ -67,7 +108,7 @@ private:
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//! Normalize distribution so that probabilities sum to unity
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void normalize();
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//! Initialize alias tables for distribution
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//! Initialize alias table for sampling
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void init_alias();
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};
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@ -82,20 +123,30 @@ public:
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//! Sample a value from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled value
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double sample(uint64_t* seed) const override;
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//! \return (sampled value, sample weight)
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std::pair<double, double> sample(uint64_t* seed) const override;
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double integral() const override { return di_.integral(); };
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//! Override set_bias as no-op (bias handled in constructor)
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void set_bias(std::unique_ptr<Distribution> bias) override {}
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// Properties
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const vector<double>& x() const { return x_; }
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const vector<double>& prob() const { return di_.prob(); }
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const vector<size_t>& alias() const { return di_.alias(); }
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const vector<double>& weight() const { return weight_; }
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protected:
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//! Sample a value (unbiased) from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled value
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double sample_unbiased(uint64_t* seed) const override;
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private:
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vector<double> x_; //!< Possible outcomes
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DiscreteIndex di_; //!< discrete probability distribution of
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//!< outcome indices
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vector<double> x_; //!< Possible outcomes
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vector<double> weight_; //!< Importance weights (empty if unbiased)
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DiscreteIndex di_; //!< Discrete probability distribution of outcome indices
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};
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//==============================================================================
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@ -107,14 +158,20 @@ public:
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explicit Uniform(pugi::xml_node node);
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Uniform(double a, double b) : a_ {a}, b_ {b} {};
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//! Sample a value from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled value
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double sample(uint64_t* seed) const override;
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//! Evaluate probability density, f(x), at a point
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//! \param x Point to evaluate f(x)
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//! \return f(x)
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double evaluate(double x) const override;
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double a() const { return a_; }
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double b() const { return b_; }
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protected:
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//! Sample a value (unbiased) from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled value
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double sample_unbiased(uint64_t* seed) const override;
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private:
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double a_; //!< Lower bound of distribution
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double b_; //!< Upper bound of distribution
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@ -131,15 +188,21 @@ public:
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: offset_ {std::pow(a, n + 1)}, span_ {std::pow(b, n + 1) - offset_},
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ninv_ {1 / (n + 1)} {};
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//! Sample a value from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled value
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double sample(uint64_t* seed) const override;
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//! Evaluate probability density, f(x), at a point
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//! \param x Point to evaluate f(x)
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//! \return f(x)
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double evaluate(double x) const override;
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double a() const { return std::pow(offset_, ninv_); }
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double b() const { return std::pow(offset_ + span_, ninv_); }
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double n() const { return 1 / ninv_ - 1; }
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protected:
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//! Sample a value (unbiased) from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled value
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double sample_unbiased(uint64_t* seed) const override;
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private:
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//! Store processed values in object to allow for faster sampling
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double offset_; //!< a^(n+1)
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@ -156,13 +219,19 @@ public:
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explicit Maxwell(pugi::xml_node node);
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Maxwell(double theta) : theta_ {theta} {};
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//! Sample a value from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled value
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double sample(uint64_t* seed) const override;
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//! Evaluate probability density, f(x), at a point
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//! \param x Point to evaluate f(x)
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//! \return f(x)
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double evaluate(double x) const override;
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double theta() const { return theta_; }
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protected:
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//! Sample a value (unbiased) from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled value
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double sample_unbiased(uint64_t* seed) const override;
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private:
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double theta_; //!< Factor in exponential [eV]
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};
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explicit Watt(pugi::xml_node node);
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Watt(double a, double b) : a_ {a}, b_ {b} {};
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//! Sample a value from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled value
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double sample(uint64_t* seed) const override;
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//! Evaluate probability density, f(x), at a point
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//! \param x Point to evaluate f(x)
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//! \return f(x)
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double evaluate(double x) const override;
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double a() const { return a_; }
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double b() const { return b_; }
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protected:
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//! Sample a value (unbiased) from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled value
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double sample_unbiased(uint64_t* seed) const override;
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private:
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double a_; //!< Factor in exponential [eV]
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double b_; //!< Factor in square root [1/eV]
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@ -200,14 +275,20 @@ public:
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Normal(double mean_value, double std_dev)
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: mean_value_ {mean_value}, std_dev_ {std_dev} {};
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//! Sample a value from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled value
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double sample(uint64_t* seed) const override;
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//! Evaluate probability density, f(x), at a point
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//! \param x Point to evaluate f(x)
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//! \return f(x)
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double evaluate(double x) const override;
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double mean_value() const { return mean_value_; }
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double std_dev() const { return std_dev_; }
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protected:
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//! Sample a value (unbiased) from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled value
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double sample_unbiased(uint64_t* seed) const override;
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private:
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double mean_value_; //!< middle of distribution [eV]
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double std_dev_; //!< standard deviation [eV]
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Tabular(const double* x, const double* p, int n, Interpolation interp,
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const double* c = nullptr);
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//! Sample a value from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled value
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double sample(uint64_t* seed) const override;
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//! Evaluate probability density, f(x), at a point
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//! \param x Point to evaluate f(x)
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//! \return f(x)
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double evaluate(double x) const override;
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// properties
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vector<double>& x() { return x_; }
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Interpolation interp() const { return interp_; }
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double integral() const override { return integral_; };
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protected:
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//! Sample a value (unbiased) from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled value
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double sample_unbiased(uint64_t* seed) const override;
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private:
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vector<double> x_; //!< tabulated independent variable
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vector<double> p_; //!< tabulated probability density
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explicit Equiprobable(pugi::xml_node node);
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Equiprobable(const double* x, int n) : x_ {x, x + n} {};
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//! Sample a value from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled value
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double sample(uint64_t* seed) const override;
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//! Evaluate probability density, f(x), at a point
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//! \param x Point to evaluate f(x)
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//! \return f(x)
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double evaluate(double x) const override;
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const vector<double>& x() const { return x_; }
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protected:
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//! Sample a value (unbiased) from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled value
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double sample_unbiased(uint64_t* seed) const override;
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private:
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vector<double> x_; //! Possible outcomes
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};
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//! Sample a value from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled value
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double sample(uint64_t* seed) const override;
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//! \return (sampled value, sample weight)
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std::pair<double, double> sample(uint64_t* seed) const override;
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double integral() const override { return integral_; }
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private:
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// Storrage for probability + distribution
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using DistPair = std::pair<double, UPtrDist>;
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//! Override set_bias as no-op (bias handled in constructor)
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void set_bias(std::unique_ptr<Distribution> bias) override {}
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vector<DistPair>
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distribution_; //!< sub-distributions + cummulative probabilities
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double integral_; //!< integral of distribution
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protected:
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//! Sample a value (unbiased) from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled value
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double sample_unbiased(uint64_t* seed) const override;
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private:
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vector<UPtrDist> distribution_; //!< Sub-distributions
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vector<double> weight_; //!< Importance weights for component selection
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DiscreteIndex di_; //!< Discrete probability distribution of indices
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double integral_; //!< Integral of distribution
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};
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} // namespace openmc
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//! Sample a direction from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Direction sampled
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virtual Direction sample(uint64_t* seed) const = 0;
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//! \return (sampled Direction, sample weight)
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virtual std::pair<Direction, double> sample(uint64_t* seed) const = 0;
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Direction u_ref_ {0.0, 0.0, 1.0}; //!< reference direction
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};
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//! Sample a direction from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Direction sampled
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Direction sample(uint64_t* seed) const override;
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//! \return (sampled Direction, sample weight)
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std::pair<Direction, double> sample(uint64_t* seed) const override;
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//! Sample a direction and return evaluation of the PDF for biased sampling.
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//! Note that bias distributions are intended to return unit-weight samples.
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//! \param seed Pseudorandom number seed points
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//! \return (sampled Direction, value of the PDF at this Direction)
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std::pair<Direction, double> sample_as_bias(uint64_t* seed) const;
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// Observing pointers
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Distribution* mu() const { return mu_.get(); }
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Distribution* phi() const { return phi_.get(); }
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private:
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//! Common sampling implementation
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//! \param seed Pseudorandom number seed pointer
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//! \param return_pdf If true, return PDF evaluation; if false, return
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//! importance weight
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//! \return (sampled Direction, weight or PDF value)
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std::pair<Direction, double> sample_impl(
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uint64_t* seed, bool return_pdf) const;
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Direction v_ref_ {1.0, 0.0, 0.0}; //!< reference direction
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Direction w_ref_;
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UPtrDist mu_; //!< Distribution of polar angle
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class Isotropic : public UnitSphereDistribution {
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public:
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Isotropic() {};
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explicit Isotropic(pugi::xml_node node);
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//! Sample a direction from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled direction
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Direction sample(uint64_t* seed) const override;
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//! \return (sampled direction, sample weight)
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std::pair<Direction, double> sample(uint64_t* seed) const override;
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// Set or get bias distribution
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void set_bias(std::unique_ptr<PolarAzimuthal> bias)
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{
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bias_ = std::move(bias);
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}
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const PolarAzimuthal* bias() const { return bias_.get(); }
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protected:
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// Biasing distribution
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unique_ptr<PolarAzimuthal> bias_;
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};
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//==============================================================================
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//! Sample a direction from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled direction
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Direction sample(uint64_t* seed) const override;
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//! \return (sampled direction, sample weight)
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std::pair<Direction, double> sample(uint64_t* seed) const override;
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};
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using UPtrAngle = unique_ptr<UnitSphereDistribution>;
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virtual ~SpatialDistribution() = default;
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//! Sample a position from the distribution
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virtual Position sample(uint64_t* seed) const = 0;
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled (position, importance weight)
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virtual std::pair<Position, double> sample(uint64_t* seed) const = 0;
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static unique_ptr<SpatialDistribution> create(pugi::xml_node node);
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};
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//! Sample a position from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled position
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Position sample(uint64_t* seed) const override;
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//! \return Sampled (position, importance weight)
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std::pair<Position, double> sample(uint64_t* seed) const override;
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// Observer pointers
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Distribution* x() const { return x_.get(); }
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//! Sample a position from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled position
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Position sample(uint64_t* seed) const override;
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//! \return Sampled (position, importance weight)
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std::pair<Position, double> sample(uint64_t* seed) const override;
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Distribution* r() const { return r_.get(); }
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Distribution* phi() const { return phi_.get(); }
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//! Sample a position from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled position
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Position sample(uint64_t* seed) const override;
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//! \return Sampled (position, importance weight)
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std::pair<Position, double> sample(uint64_t* seed) const override;
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Distribution* r() const { return r_.get(); }
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Distribution* cos_theta() const { return cos_theta_.get(); }
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@ -109,8 +111,8 @@ public:
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//! Sample a position from the distribution
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//! \param seed Pseudorandom number seed pointer
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//! \return Sampled position
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Position sample(uint64_t* seed) const override;
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//! \return Sampled (position, importance weight)
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std::pair<Position, double> sample(uint64_t* seed) const override;
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//! Sample the mesh for an element and position within that element
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//! \param seed Pseudorandom number seed pointer
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@ -133,8 +135,8 @@ public:
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private:
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int32_t mesh_idx_ {C_NONE};
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DiscreteIndex elem_idx_dist_; //!< Distribution of
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//!< mesh element indices
|
||||
DiscreteIndex elem_idx_dist_; //!< Distribution of mesh element indices
|
||||
vector<double> weight_; //!< Importance weights (empty if unbiased)
|
||||
};
|
||||
|
||||
//==============================================================================
|
||||
|
|
@ -149,12 +151,13 @@ public:
|
|||
|
||||
//! Sample a position from the distribution
|
||||
//! \param seed Pseudorandom number seed pointer
|
||||
//! \return Sampled position
|
||||
Position sample(uint64_t* seed) const override;
|
||||
//! \return Sampled (position, importance weight)
|
||||
std::pair<Position, double> sample(uint64_t* seed) const override;
|
||||
|
||||
private:
|
||||
std::vector<Position> point_cloud_;
|
||||
DiscreteIndex point_idx_dist_; //!< Distribution of Position indices
|
||||
vector<double> weight_; //!< Importance weights (empty if unbiased)
|
||||
};
|
||||
|
||||
//==============================================================================
|
||||
|
|
@ -167,8 +170,8 @@ public:
|
|||
|
||||
//! Sample a position from the distribution
|
||||
//! \param seed Pseudorandom number seed pointer
|
||||
//! \return Sampled position
|
||||
Position sample(uint64_t* seed) const override;
|
||||
//! \return Sampled (position, importance weight)
|
||||
std::pair<Position, double> sample(uint64_t* seed) const override;
|
||||
|
||||
// Properties
|
||||
bool only_fissionable() const { return only_fissionable_; }
|
||||
|
|
@ -193,8 +196,8 @@ public:
|
|||
|
||||
//! Sample a position from the distribution
|
||||
//! \param seed Pseudorandom number seed pointer
|
||||
//! \return Sampled position
|
||||
Position sample(uint64_t* seed) const override;
|
||||
//! \return Sampled (position, importance weight)
|
||||
std::pair<Position, double> sample(uint64_t* seed) const override;
|
||||
|
||||
Position r() const { return r_; }
|
||||
|
||||
|
|
|
|||
|
|
@ -217,8 +217,8 @@ public:
|
|||
|
||||
//! Sample a position from the distribution
|
||||
//! \param seed Pseudorandom number seed pointer
|
||||
//! \return Sampled position
|
||||
Position sample(uint64_t* seed) const override;
|
||||
//! \return (sampled position, importance weight)
|
||||
std::pair<Position, double> sample(uint64_t* seed) const override;
|
||||
|
||||
private:
|
||||
int32_t mesh_index_ {C_NONE}; //!< Index in global meshes array
|
||||
|
|
|
|||
Loading…
Add table
Add a link
Reference in a new issue