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reverse mode automatic differentiation
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pareto_cdf_log.hpp
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1 #ifndef STAN_MATH_PRIM_SCAL_PROB_PARETO_CDF_LOG_HPP
2 #define STAN_MATH_PRIM_SCAL_PROB_PARETO_CDF_LOG_HPP
3 
4 #include <boost/random/exponential_distribution.hpp>
5 #include <boost/random/variate_generator.hpp>
15 #include <cmath>
16 #include <limits>
17 
18 namespace stan {
19  namespace math {
20 
21  template <typename T_y, typename T_scale, typename T_shape>
22  typename return_type<T_y, T_scale, T_shape>::type
23  pareto_cdf_log(const T_y& y, const T_scale& y_min, const T_shape& alpha) {
25  T_partials_return;
26 
27  // Size checks
28  if ( !( stan::length(y) && stan::length(y_min) && stan::length(alpha) ) )
29  return 0.0;
30 
31  // Check errors
32  static const char* function("stan::math::pareto_cdf_log");
33 
40  using std::log;
41  using std::exp;
42 
43  T_partials_return P(0.0);
44 
45  check_not_nan(function, "Random variable", y);
46  check_nonnegative(function, "Random variable", y);
47  check_positive_finite(function, "Scale parameter", y_min);
48  check_positive_finite(function, "Shape parameter", alpha);
49  check_consistent_sizes(function,
50  "Random variable", y,
51  "Scale parameter", y_min,
52  "Shape parameter", alpha);
53 
54  // Wrap arguments in vectors
55  VectorView<const T_y> y_vec(y);
56  VectorView<const T_scale> y_min_vec(y_min);
57  VectorView<const T_shape> alpha_vec(alpha);
58  size_t N = max_size(y, y_min, alpha);
59 
61  operands_and_partials(y, y_min, alpha);
62 
63  // Explicit return for extreme values
64  // The gradients are technically ill-defined, but treated as zero
65 
66  for (size_t i = 0; i < stan::length(y); i++) {
67  if (value_of(y_vec[i]) < value_of(y_min_vec[i]))
68  return operands_and_partials.to_var(stan::math::negative_infinity(),
69  y, y_min, alpha);
70  }
71 
72  // Compute vectorized cdf_log and its gradients
73 
74  for (size_t n = 0; n < N; n++) {
75  // Explicit results for extreme values
76  // The gradients are technically ill-defined, but treated as zero
77  if (value_of(y_vec[n]) == std::numeric_limits<double>::infinity()) {
78  return operands_and_partials.to_var(0.0, y, y_min, alpha);
79  }
80 
81  // Pull out values
82  const T_partials_return log_dbl = log(value_of(y_min_vec[n])
83  / value_of(y_vec[n]));
84  const T_partials_return y_min_inv_dbl = 1.0 / value_of(y_min_vec[n]);
85  const T_partials_return alpha_dbl = value_of(alpha_vec[n]);
86 
87  // Compute
88  const T_partials_return Pn = 1.0 - exp(alpha_dbl * log_dbl);
89 
90  P += log(Pn);
91 
93  operands_and_partials.d_x1[n]
94  += alpha_dbl * y_min_inv_dbl * exp((alpha_dbl + 1) * log_dbl) / Pn;
96  operands_and_partials.d_x2[n]
97  -= alpha_dbl * y_min_inv_dbl * exp(alpha_dbl * log_dbl) / Pn;
99  operands_and_partials.d_x3[n]
100  -= exp(alpha_dbl * log_dbl) * log_dbl / Pn;
101  }
102 
103  return operands_and_partials.to_var(P, y, y_min, alpha);
104  }
105  }
106 }
107 #endif
bool check_greater_or_equal(const char *function, const char *name, const T_y &y, const T_low &low)
Return true if y is greater or equal than low.
bool check_not_nan(const char *function, const char *name, const T_y &y)
Return true if y is not NaN.
T value_of(const fvar< T > &v)
Return the value of the specified variable.
Definition: value_of.hpp:16
fvar< T > log(const fvar< T > &x)
Definition: log.hpp:15
size_t length(const std::vector< T > &x)
Definition: length.hpp:10
T_return_type to_var(T_partials_return logp, const T1 &x1=0, const T2 &x2=0, const T3 &x3=0, const T4 &x4=0, const T5 &x5=0, const T6 &x6=0)
VectorView< T_partials_return, is_vector< T1 >::value, is_constant_struct< T1 >::value > d_x1
Metaprogram to determine if a type has a base scalar type that can be assigned to type double...
fvar< T > exp(const fvar< T > &x)
Definition: exp.hpp:10
VectorView< T_partials_return, is_vector< T3 >::value, is_constant_struct< T3 >::value > d_x3
A variable implementation that stores operands and derivatives with respect to the variable...
size_t max_size(const T1 &x1, const T2 &x2)
Definition: max_size.hpp:9
bool check_consistent_sizes(const char *function, const char *name1, const T1 &x1, const char *name2, const T2 &x2)
Return true if the dimension of x1 is consistent with x2.
VectorView< T_partials_return, is_vector< T2 >::value, is_constant_struct< T2 >::value > d_x2
return_type< T_y, T_scale, T_shape >::type pareto_cdf_log(const T_y &y, const T_scale &y_min, const T_shape &alpha)
bool check_nonnegative(const char *function, const char *name, const T_y &y)
Return true if y is non-negative.
VectorView is a template metaprogram that takes its argument and allows it to be used like a vector...
Definition: VectorView.hpp:41
boost::math::tools::promote_args< typename partials_type< typename scalar_type< T1 >::type >::type, typename partials_type< typename scalar_type< T2 >::type >::type, typename partials_type< typename scalar_type< T3 >::type >::type, typename partials_type< typename scalar_type< T4 >::type >::type, typename partials_type< typename scalar_type< T5 >::type >::type, typename partials_type< typename scalar_type< T6 >::type >::type >::type type
bool check_positive_finite(const char *function, const char *name, const T_y &y)
Return true if y is positive and finite.
double negative_infinity()
Return negative infinity.
Definition: constants.hpp:132

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