\(\newcommand{\B}[1]{ {\bf #1} }\) \(\newcommand{\R}[1]{ {\rm #1} }\) \(\newcommand{\W}[1]{ \; #1 \; }\)

user_hes_fixed_math.py

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Check the Hessian of the Fixed Effects Objective

Purpose

This is a detailed mathematical explanation of computing Hessian of the fixed effects objective used by the asymptotic sampling method.

Reference

See the theory section of the cppad_mixed documentation.

Notation

\(\theta\)	model incidence for the parent region
\(u_0\)	incidence random effect for first child
\(u_1\)	incidence random effect for second child
\(y_0\)	measured incidence for the first child
\(y_1\)	measured incidence for the second child
\(s\)	standard deviation for data and random effects

The only fixed effect in this model is \(\theta\) (sometimes written theta ) the incidence level for the world. The random effects are \(u_0\) and \(u_1\).

Problem Parameters

import math
import time
theta_true     = 0.5
u_true         = [ 0.5, -0.5 ]
y_0            = theta_true * math.exp( u_true[0] )
y_1            = theta_true * math.exp( u_true[1] )
standard_dev   = theta_true # the standard deviation s
random_seed    = int( time.time() )
number_sample  = 1000
eta_in_prior   = 1e-6 # if None, the fixed effects are not scaled

Random Likelihood

The negative log-likelihood for this example, ignoring the constant of integration, is

\[f( \theta, u ) = \frac{1}{2 s^2} \left( [ y_0 - \theta \exp( u_0 ) ]^2 + [ y_1 - \theta \exp( u_1 ) ]^2 + u_0^2 + u_1^2 \right)\]

Gradient w.r.t. Fixed Effects

\[f_\theta ( \theta, u ) = \frac{1}{s^2} [ \theta \exp( 2 u_0 ) - y_0 \exp( u_0 ) + \theta \exp( 2 u_1 ) - y_1 \exp( u_1 ) ]\]

Gradient w.r.t. Random Effects

\[\begin{split}f_u ( \theta, u ) = \frac{1}{s^2} \left( \begin{array}{c} \theta^2 \exp( 2 u_0 ) - y_0 \theta \exp( u_0 ) + u_0 \\ \theta^2 \exp( 2 u_1 ) - y_1 \theta \exp( u_1 ) + u_1 \end{array} \right)\end{split}\]

Hessian w.r.t. Fixed Effects

\[f_{\theta,\theta} ( \theta, u ) = \frac{1}{s^2} [ \exp( 2 u_0 ) + \exp( 2 u_1 ) ]\]

Hessian w.r.t. Random Effects

\[\begin{split}f_{u,u} ( \theta, u ) = \frac{1}{s^2} \left( \begin{array}{cc} 2 \theta^2 \exp( 2 u_0 ) - y_0 \theta \exp( u_0 ) + 1 & 0 \\ 0 & 2 \theta^2 \exp( 2 u_1 ) - y_1 \theta \exp( u_1 ) + 1 \end{array} \right)\end{split}\]

Hessian Cross Term

\[\begin{split}f_{u,\theta} ( \theta, u ) = \frac{1}{s^2} \left( \begin{array}{c} 2 \theta \exp( 2 u_0 ) - y_0 \exp( u_0 ) \\ 2 \theta \exp( 2 u_1 ) - y_1 \exp( u_1 ) \end{array} \right)\end{split}\]

Optimal Random Effects

Implicit Function Definition

The optimal random effects \(\hat{u} ( \theta )\) solve the equation

\[f_u [ \theta , \hat{u} ( \theta ) ] = 0\]

Derivatives of Optimal Random Effects

Using the implicit function theorem we have

\[\hat{u}^{(1)} ( \theta )= - f_{u,u} [ \theta , \hat{u} ( \theta) ]^{-1} f_{u,\theta} [ \theta , \hat{u} ( \theta) ]\]

Substituting in the formulas above for the Hessian terms on the right hand side we obtain:

\[\hat{u}_i^{(1)} ( \theta ) = - \frac{ 2 \theta \exp[ 2 \hat{u}_i ( \theta) ] - y_i \exp[ \hat{u}_i ( \theta) ] }{ 2 \theta^2 \exp[ 2 \hat{u}_i ( \theta) ] - y_i \theta \exp[ \hat{u}_i ( \theta) ] + 1 }\]

We can compute \(\hat{u}_i ( \theta )\) by optimizing the random effects corresponding to the fixed effects being \(\theta\). We define \(g_i ( \theta )\) by the equation

\[g_i ( \theta ) = 2 \theta \exp[ 2 \hat{u}_i ( \theta) ] - y_i \exp[ \hat{u}_i ( \theta ) ]\]

Give \(\hat{u}_i ( \theta )\) we can compute \(g_i ( \theta )\). Given \(g_i ( \theta )\), we can compute the derivative \(\hat{u}_i^{(1)} ( \theta )\) using

\[\hat{u}_i^{(1)} ( \theta ) = - \frac{ g_i ( \theta ) }{ \theta g_i ( \theta ) + 1}\]

Given \(\hat{u}^{(1)} ( \theta )\), we can compute the derivative \(g_i^{(1)} ( \theta )\) using

\[g_i^{(1)} ( \theta ) = 2 \exp[ 2 \hat{u}_i ( \theta) ] + \left( 4 \theta \exp [ 2 \hat{u}_i ( \theta ) ] - y_i \exp [ \hat{u}_i ( \theta ) ] \right) \hat{u}_i^{(1)} ( \theta )\]

Given \(g_i^{(1)} ( \theta )\), we can compute the second derivative \(\hat{u}_i^{(2)} ( \theta )\) using

\[\hat{u}_i^{(2)} ( \theta ) = \frac{ g_i ( \theta ) [ g_i ( \theta ) + \theta g_i ^{(1)} ( \theta ) ] } { [ \theta g_i ( \theta ) + 1 ]^2 } - \frac{ g_i ^{(1)}( \theta ) }{ \theta g_i ( \theta ) + 1}\]

\[\hat{u}_i^{(2)} ( \theta ) = \frac{ g_i ( \theta )^2 - g_i ^{(1)}( \theta )} { [ \theta g_i ( \theta ) + 1 ]^2 }\]

Given \(\hat{u}^{(2)} ( \theta )\), we can compute the second derivative \(g_i^{(2)} ( \theta )\) using

\begin{eqnarray} g_i^{(2)} ( \theta ) & = & 8 \exp[ 2 \hat{u}_i ( \theta) ] \hat{u}_i^{(1)} ( \theta ) \\ & + & \left( 8 \theta \exp [ 2 \hat{u}_i ( \theta ) ] - y_i \exp [ \hat{u}_i ( \theta ) ] \right) \hat{u}_i^{(1)} ( \theta )^2 \\ & + & \left( 4 \theta \exp [ 2 \hat{u}_i ( \theta ) ] - y_i \exp [ \hat{u}_i ( \theta ) ] \right) \hat{u}_i^{(2)} ( \theta ) \end{eqnarray}

Laplace Approximation

Up to a constant, the Laplace approximation (fixed effects objective), as a function of the fixed effects, is:

\[L ( \theta ) = F( \theta ) + G( \theta )\]

where \(F( \theta )\) and \(G( \theta )\) are defined by

\[F( \theta ) = f[ \theta , \hat{u} ( \theta ) ]\]

\[G( \theta ) =\frac{1}{2} \log \det f_{u,u} [ \theta , \hat{u} ( \theta ) ]\]

The derivative of \(F( \theta )\) is given by

\[F^{(1)} ( \theta ) = f_\theta [ \theta , \hat{u} ( \theta ) ] + f_u [ \theta , \hat{u} ( \theta ) ] \hat{u}^{(1)} ( \theta )\]

It follows from the definition of \(\hat{u} ( \theta )\) that \(f_u [ \theta , \hat{u} ( \theta ) ] = 0\) and

\[F^{(1)} ( \theta ) = f_\theta [ \theta , \hat{u} ( \theta ) ]\]

Taking the derivative of the equation above we obtain

\[F^{(2)} ( \theta ) = f_{\theta,\theta} [ \theta , \hat{u} ( \theta ) ] + f_{\theta,u} [ \theta , \hat{u} ( \theta ) ] \hat{u}^{(1)} ( \theta )\]

Combining the definition of \(G( \theta )\), \(g_i ( \theta )\) and the formula for \(f_{u,u} ( \theta , u )\) we have

\[\begin{split}G( \theta ) = \frac{1}{2} \log \det \left( \begin{array}{cc} [ \theta g_0 ( \theta ) + 1 ] / s^2 & 0 \\ 0 & [ \theta g_1 ( \theta ) + 1 ] / s^2 \end{array} \right)\end{split}\]

Defining \(h_i ( \theta )\) by

\[h_i ( \theta ) = \theta g_i ( \theta ) + 1\]

we obtain the representation

\[G ( \theta ) = + \frac{1}{2} \left( \log [ h_0 ( \theta ) ] + \log [ h_1 ( \theta ) ] - \log ( s^4 ) \right)\]

The first and second derivative of \(h_i ( \theta )\) and \(G( \theta )\) are given by

\[h_i^{(1)} ( \theta ) = g_i ( \theta ) + \theta g_i^{(1)} ( \theta )\]

\[G^{(1)} ( \theta ) = \frac{1}{2} \left( \frac{ h_0^{(1)} ( \theta ) }{ h_0 ( \theta ) } + \frac{ h_1^{(1)} ( \theta ) }{ h_1 ( \theta ) } \right)\]

\[h_i^{(2)} ( \theta ) = 2 g_i^{(1)} ( \theta ) + \theta g_i^{(2)} ( \theta )\]

\[G^{(2)} ( \theta ) = \frac{1}{2} \left( \frac{ h_0 ( \theta ) h_0^{(2)} ( \theta ) - h_0^{(1)} ( \theta )^2 } { h_0 ( \theta )^2 } + \frac{ h_1 ( \theta ) h_1^{(2)} ( \theta ) - h_1^{(1)} ( \theta )^2 } { h_1 ( \theta )^2 } \right)\]

Asymptotic Statistics

The asymptotic posterior distribution for the optimal estimate of \(\theta\) give the data \(y\) is a normal with variance equal to the inverse of

\[L^{(2)} ( \theta ) = F^{(2)} ( \theta ) + G^{(2)} ( \theta )\]

Scaling Fixed Effects

If eta is not null, the Hessian is with respect to \(\alpha = \log( \theta + \eta )\). Inverting this relation we define \(\theta ( \alpha ) = \exp( \alpha ) - \eta\). The fixed effects objective as a function of \(\alpha\) is

\[H( \alpha ) = L[ \theta ( \alpha ) ] = F[ \theta( \alpha ) ] + G[ \theta( \alpha ) ]\]

Taking the first and second derivatives, we have

\[H^{(1)}( \alpha ) = \left( F^{(1)}[ \theta( \alpha ) ] + G^{(1)}[ \theta( \alpha ) ] \right) \exp( \alpha )\]

\begin{eqnarray} H^{(2)}( \alpha ) & = & \left( F^{(1)}[ \theta( \alpha ) ] + G^{(1)}[ \theta( \alpha ) ] \right) \exp( \alpha ) \\ & + & \left( F^{(2)}[ \theta( \alpha ) ] + G^{(2)}[ \theta( \alpha ) ] \right) \exp( 2 \alpha ) \end{eqnarray}

Optimal Fixed Effects

The first order necessary conditions for \(\hat{\alpha}\) to be a minimizer of the fixed effects object is \(H^{(1)} ( \hat{\alpha} ) = 0\). In this case we can simplify the Hessian scaling as follows:

\begin{eqnarray} H^{(2)}( \hat{\alpha} ) & = & \left( F^{(2 }( \hat{\theta} ) + G^{(2)}( \hat{\theta} ) \right) \exp( 2 \hat{\alpha} ) \\ & = & L^{(2)} ( \hat{\theta} ) \exp( 2 \hat{\alpha} ) \end{eqnarray}

where \(\hat{\theta} = \theta( \hat{\alpha} )\).

Source Code

import numpy
import sys
import os
import copy
test_program = 'example/user/hes_fixed_math.py'
if sys.argv[0] != test_program  or len(sys.argv) != 1 :
   usage  = 'python3 ' + test_program + '\n'
   usage += 'where python3 is the python 3 program on your system\n'
   usage += 'and working directory is the dismod_at distribution directory\n'
   sys.exit(usage)
print(test_program)
#
# import dismod_at
local_dir = os.getcwd() + '/python'
if( os.path.isdir( local_dir + '/dismod_at' ) ) :
   sys.path.insert(0, local_dir)
import dismod_at
#
# change into the build/example/user directory
if not os.path.exists('build/example/user') :
   os.makedirs('build/example/user')
os.chdir('build/example/user')
#
def example_db (file_name) :
   def fun_rate_child(a, t) :
      return ('prior_gauss_zero', None, None)
   def fun_rate_parent(a, t) :
      return ('prior_rate_parent', None, None)
   # ----------------------------------------------------------------------
   # age table
   age_list    = [    0.0,   100.0 ]
   #
   # time table
   time_list   = [ 1995.0,  2015.0 ]
   #
   # integrand table
   integrand_table = [ { 'name':'Sincidence' } ]
   #
   node_table = [
      { 'name':'world',    'parent':''       },
      { 'name':'child_0',  'parent':'world'  },
      { 'name':'child_1',  'parent':'world'  },
   ]
   #
   # weight table:
   weight_table = list()
   #
   # covariate table: no covriates
   covariate_table = list()
   #
   # mulcov table
   mulcov_table = list()
   #
   # avgint table:
   avgint_table = list()
   #
   # nslist_dict:
   nslist_dict = dict()
   # ----------------------------------------------------------------------
   # data table:
   data_table = list()
   row = {
      'node':        'child_0',
      'subgroup':    'world',
      'density':     'gaussian',
      'weight':      '',
      'hold_out':     False,
      'time_lower':   2000.0,
      'time_upper':   2000.0,
      'age_lower':    50.0,
      'age_upper':    50.0,
      'integrand':   'Sincidence',
      'meas_value':   y_0,
      'meas_std':     standard_dev,
   }
   data_table.append( copy.copy(row) )
   #
   row['node']       = 'child_1'
   row['meas_value'] = y_1
   data_table.append( copy.copy(row) )
   #
   # ----------------------------------------------------------------------
   # prior_table
   prior_table = [
      { # prior_rate_parent
         'name':     'prior_rate_parent',
         'density':  'uniform',
         'lower':    1e-2 * theta_true,
         'upper':    1e+2 * theta_true,
         'mean':     theta_true / 3.0, # only used for start and scale
         'eta':      eta_in_prior,
      },{ # prior_gauss_zero
         'name':     'prior_gauss_zero',
         'density':  'gaussian',
         'mean':     0.0,
         'std':      standard_dev,
      }
   ]
   # ----------------------------------------------------------------------
   # smooth table
   smooth_table = [
      { # smooth_rate_parent
         'name':                     'smooth_rate_parent',
         'age_id':                   [ 0 ],
         'time_id':                  [ 0 ],
         'fun':                      fun_rate_parent
      }, { # smooth_rate_child
         'name':                     'smooth_rate_child',
         'age_id':                   [ 0 ],
         'time_id':                  [ 0 ],
         'fun':                      fun_rate_child
      }
   ]
   # ----------------------------------------------------------------------
   # rate table
   rate_table = [
      {
         'name':          'iota',
         'parent_smooth': 'smooth_rate_parent',
         'child_smooth':  'smooth_rate_child',
      }
   ]
   # ----------------------------------------------------------------------
   # option_table
   option_table = [
      { 'name':'parent_node_name',       'value':'world'              },
      { 'name':'ode_step_size',          'value':'10.0'               },
      { 'name':'random_seed',            'value':str(random_seed)     },
      { 'name':'rate_case',              'value':'iota_pos_rho_zero'  },

      { 'name':'quasi_fixed',            'value':'true'               },
      { 'name':'derivative_test_fixed',  'value':'none'               },
      { 'name':'max_num_iter_fixed',     'value':'100'                },
      { 'name':'print_level_fixed',      'value':'0'                  },
      { 'name':'tolerance_fixed',        'value':'1e-12'              },

      { 'name':'derivative_test_random', 'value':'none'               },
      { 'name':'max_num_iter_random',    'value':'100'                },
      { 'name':'print_level_random',     'value':'0'                  },
      { 'name':'tolerance_random',       'value':'1e-12'              }
   ]
   # ----------------------------------------------------------------------
   # subgroup_table
   subgroup_table = [ { 'subgroup':'world', 'group':'world' } ]
   # ----------------------------------------------------------------------
   # create database
   dismod_at.create_database(
      file_name,
      age_list,
      time_list,
      integrand_table,
      node_table,
      subgroup_table,
      weight_table,
      covariate_table,
      avgint_table,
      data_table,
      prior_table,
      smooth_table,
      nslist_dict,
      rate_table,
      mulcov_table,
      option_table
   )
# ===========================================================================
file_name  = 'example.db'
example_db(file_name)
#
program   = '../../devel/dismod_at'
dismod_at.system_command_prc([ program, file_name, 'init' ])
dismod_at.system_command_prc([ program, file_name, 'fit', 'both' ])
dismod_at.system_command_prc(
   [ program, file_name, 'sample', 'asymptotic', 'both', str(number_sample) ]
)
# -----------------------------------------------------------------------
# get tables
connection    = dismod_at.create_connection(
   file_name, new = False, readonly = True
)
var_table     = dismod_at.get_table_dict(connection, 'var')
node_table    = dismod_at.get_table_dict(connection, 'node')
rate_table    = dismod_at.get_table_dict(connection, 'rate')
fit_var_table = dismod_at.get_table_dict(connection, 'fit_var')
sample_table  = dismod_at.get_table_dict(connection, 'sample')
hes_fixed_table = dismod_at.get_table_dict(connection, 'hes_fixed')
connection.close()
dismod_at.db2csv_command(file_name)
# -----------------------------------------------------------------------
# node_name2var_id
node_name2var_id = dict()
assert len(var_table) == 3
for var_id in range(len(var_table) ) :
   assert var_id < 3
   row = var_table[var_id]
   assert row['var_type'] == 'rate'
   assert rate_table[row['rate_id']]['rate_name']  == 'iota'
   node_name = node_table[row['node_id']]['node_name']
   node_name2var_id[node_name] = var_id
# -----------------------------------------------------------------------
# uhat(theta)
def optimal_random_effect(fixed_effect) :
   #
   # set start_var value for the fixed effects
   var_id = node_name2var_id['world']
   sql_cmd  = 'UPDATE start_var SET start_var_value = ' + str(fixed_effect)
   sql_cmd += ' WHERE start_var_id == ' + str(var_id)
   connection    = dismod_at.create_connection(
      file_name, new = False, readonly = False
   )
   dismod_at.sql_command(connection, sql_cmd)
   connection.close()
   #
   # optimize the random effects
   dismod_at.system_command_prc([ program, file_name, 'fit', 'random' ])
   #
   # retrieve the optimal random effects
   connection    = dismod_at.create_connection(
      file_name, new = False, readonly = True
   )
   fit_var_table = dismod_at.get_table_dict(connection, 'fit_var')
   #
   var_id        = node_name2var_id['child_0']
   uhat_0        = fit_var_table[var_id]['fit_var_value']
   #
   var_id        = node_name2var_id['child_1']
   uhat_1        = fit_var_table[var_id]['fit_var_value']
   #
   uhat          = numpy.array( [ uhat_0, uhat_1 ] )
   return uhat
# ------------------------------------------------------------------------
# f(theta, u)
def random_likelihood(fixed_effect, random_effect) :
   theta    = fixed_effect
   u        = random_effect
   y        = numpy.array( [y_0, y_1] )
   residual = y - theta * numpy.exp(u)
   residual = numpy.append(residual, u)
   sum_sq   = numpy.sum( residual * residual )
   return sum_sq / (2.0 * standard_dev * standard_dev)
# -----------------------------------------------------------------------
# log det f_{u,u} ( theta , u )
def log_det_random_hessian(fixed_effect, random_effect) :
   theta    = fixed_effect
   u        = random_effect
   exp_u    = numpy.exp( u )
   exp_2u   = numpy.exp( 2.0 * u )
   g        = 2.0 * theta * exp_2u - y * exp_u
   h        = theta * g + 1.0
   s_sq     = standard_dev * standard_dev
   log_det  = numpy.sum( numpy.log(h / s_sq) )
   return log_det
# -----------------------------------------------------------------------
def check_rel_error(check, value, tolerance) :
   rel_error = abs( check / value - 1.0 )
   # print(rel_error, tolerance)
   if numpy.isscalar( rel_error ) :
      ok = rel_error < tolerance
   else :
      ok = all( rel_error < tolerance )
   if not ok :
      print("random_seed =", random_seed)
   assert ok
# -----------------------------------------------------------------------
# Some values
#
# s_sq
s_sq         = standard_dev * standard_dev
#
# y
y            = numpy.array( [ y_0, y_1 ] )
#
# optimal theta (from the fit_var table)
var_id       = node_name2var_id['world']
theta        = fit_var_table[var_id]['fit_var_value']
#
# delta_theta
delta_theta  = theta / 1000.0
theta_plus   = theta + delta_theta
theta_minus  = theta - delta_theta
#
# uhat
uhat         = optimal_random_effect(theta)
uhat_plus    = optimal_random_effect(theta_plus)
uhat_minus   = optimal_random_effect(theta_minus)
#
# exp_u
exp_u        = numpy.exp( uhat )
exp_u_plus   = numpy.exp( uhat_plus )
exp_u_minus  = numpy.exp( uhat_minus )
#
# exp_2u
exp_2u       = numpy.exp( 2.0 * uhat )
exp_2u_plus  = numpy.exp( 2.0 * uhat_plus )
exp_2u_minus = numpy.exp( 2.0 * uhat_minus )
#
# g(theta)
g            = 2.0 * theta * exp_2u - y * exp_u
g_plus       = 2.0 * theta_plus * exp_2u_plus - y * exp_u_plus
g_minus      = 2.0 * theta_minus * exp_2u_minus - y * exp_u_minus
#
# h(theta)
h = theta * g + 1
#
# F(theta)
F       = random_likelihood(theta, uhat)
F_plus  = random_likelihood(theta_plus, uhat_plus)
F_minus = random_likelihood(theta_minus, uhat_minus)
#
# G(theta)
G       = log_det_random_hessian(theta, uhat) / 2.0
G_plus  = log_det_random_hessian(theta_plus, uhat_plus) / 2.0
G_minus = log_det_random_hessian(theta_minus, uhat_minus) / 2.0
#
# L(theta)
L       = F + G
L_plus  = F_plus + G_plus
L_minus = F_minus + G_minus
#
# f_u (theta, uhat)
f_u     = ( theta * theta * exp_2u - theta * y  * exp_u  + uhat ) / s_sq
#
# f_theta (theta, uhat)
f_theta = numpy.sum(theta * exp_2u - y * exp_u) / s_sq
#
# f_{theta,theta} ( theta , uhat )
f_theta_theta = numpy.sum( exp_2u ) / s_sq
#
# f_{theta, u} ( theta , uhat )
f_theta_u = ( 2 * theta * exp_2u - y * exp_u ) / s_sq
#
# dF_dtheta = F^{(1)} ( theta )
dF_dtheta = f_theta
#
# duhat_dtheta = uhat^{(1)} ( theta )
duhat_dtheta = - g / (theta * g + 1)
#
# dg_dtheta = g^{(1)} ( theta )
dg_dtheta  = 2.0 * exp_2u + (4.0 * theta * exp_2u - y * exp_u) * duhat_dtheta
#
# d2uhat_dtheta = uhat^{(2)} ( theta )
d2uhat_d2theta = (g * g - dg_dtheta) / ( (theta * g + 1) * (theta * g + 1) )
#
# d2F_d2theta = F^{(2)} ( theta )
d2F_d2theta  = f_theta_theta
d2F_d2theta += numpy.dot( f_theta_u, duhat_dtheta )
#
# dh_dtheta = h^{(1)} ( theta )
dh_dtheta = g + theta * dg_dtheta
#
# dG_dtheta = G^{(1)} ( theta )
dG_dtheta = numpy.sum( dh_dtheta / h ) / 2.0
#
# d2g_d2theta = g^{(2)} ( theta )
duhat_dtheta_sq = duhat_dtheta * duhat_dtheta
d2g_d2theta     = 8.0 * exp_2u * duhat_dtheta
d2g_d2theta    += (8.0 * theta * exp_2u - y * exp_u) * duhat_dtheta_sq
d2g_d2theta    += (4.0 * theta * exp_2u - y * exp_u) * d2uhat_d2theta
#
# dh2_d2theta = h^{(2)} ( theta )
d2h_d2theta = 2.0 * dg_dtheta + theta * d2g_d2theta
#
# d2G_d2theta = G^{(2)} ( theta )
d2G_d2theta = (h * d2h_d2theta - dh_dtheta * dh_dtheta) / (2.0 * h * h)
d2G_d2theta = numpy.sum( d2G_d2theta )
# ----------------------------------------------------------------------------
# check that f_u ( theta , uhat ) = 0
assert all( abs(f_u) < 1e-13 )
#
# check that dF_dtheta + dG_dtheta = 0
assert abs( dF_dtheta + dG_dtheta ) < 1e-11
#
# check duhat_dtheta
check      = (uhat_plus - uhat_minus) / (2.0 * delta_theta)
check_rel_error(check, duhat_dtheta, 1e-5)
#
# check dg_dtheta
check      = (g_plus - g_minus) / (2.0 * delta_theta)
check_rel_error(check, dg_dtheta, 1e-6)
#
# check d2uhat_d2theta
check = (uhat_plus - 2.0 * uhat + uhat_minus) / (delta_theta * delta_theta)
check_rel_error(check, d2uhat_d2theta, 1e-6)
#
# check d2F_d2theta
check = (F_plus - 2.0 * F + F_minus) / (delta_theta * delta_theta)
check_rel_error(check, d2F_d2theta, 1e-6)
#
# check dG_dtheta
check   = (G_plus - G_minus) / (2.0 * delta_theta)
check_rel_error(check, dG_dtheta, 1e-6)
#
check        = (g_plus - 2.0 * g + g_minus) / (delta_theta * delta_theta)
check_rel_error(check, d2g_d2theta, 1e-6)
#
# check d2G_d2theta
check = (G_plus - 2.0 * G + G_minus) / (delta_theta * delta_theta)
check_rel_error(check, d2G_d2theta, 1e-5)
# ============================================================================
# check the Hessian of the fixed effects objective
#
# The world rate for incidence is the only fixed effect
world_var_id = node_name2var_id['world']
assert len(hes_fixed_table) == 1
row = hes_fixed_table[0]
assert row['row_var_id'] == world_var_id
assert row['col_var_id'] == world_var_id
hes_fixed_value = row['hes_fixed_value']
if eta_in_prior == None :
   dL2_d2theta     = d2F_d2theta + d2G_d2theta
   check_rel_error(dL2_d2theta, hes_fixed_value, 1e-14)
else :
   alpha        = math.log(theta + eta_in_prior)
   exp_alpha    = math.exp(alpha)
   exp_2alpha   = math.exp( 2.0 * alpha )
   dL_dtheta    = dF_dtheta + dG_dtheta
   d2L_d2theta  = d2F_d2theta + d2G_d2theta
   d2H_d2alpha  = dL_dtheta * exp_alpha + d2L_d2theta * exp_2alpha
   check_rel_error(d2H_d2alpha, hes_fixed_value, 1e-14)
#
# compute sample statistics
assert  len(sample_table) == number_sample * len(var_table)
sample_array  = numpy.zeros(number_sample, dtype = float)
for row in sample_table :
   if row['var_id'] == var_id :
      sample_index = row['sample_index']
      if eta_in_prior == None :
         sample_value = row['var_value']
      else :
         sample_value = math.log( row['var_value'] + eta_in_prior )
      sample_array[sample_index] = sample_value
sample_avg = numpy.average(sample_array)
sample_var = numpy.var(sample_array, ddof=1)
#
# check sample statistics
if eta_in_prior == None :
   check_rel_error(theta,   sample_avg,  1e-1)
else :
   check_rel_error(math.log(theta + eta_in_prior),   sample_avg,  1e-1)
check_rel_error(1.0 / hes_fixed_value, sample_var, 1e-1)
#
print('hes_fixed_math.py: OK')