#######################################
#
# File: 21probit.py
# Author: Michel Bierlaire, EPFL
# Date: Tue Aug 9 07:56:18 2011
#
#######################################
from biogeme import *
from headers import *
from loglikelihood import *
from statistics import *
# This estimates a binary probit model. All observations where Swissmetro was chosen are discarded
#Parameters to be estimated
# Arguments:
# 1 Name for report. Typically, the same as the variable
# 2 Starting value
# 3 Lower bound
# 4 Upper bound
# 5 0: estimate the parameter, 1: keep it fixed
ASC_CAR = Beta('ASC_CAR',0,-10,10,0,'Car cte.')
ASC_TRAIN = Beta('ASC_TRAIN',0,-10,10,1,'Train cte.')
B_TIME = Beta('B_TIME',0,-10,10,0,'Travel time')
B_COST = Beta('B_COST',0,-10,10,0,'Travel cost')
# Utility functions
#If the person has a GA (season ticket) her incremental cost is actually 0
#rather than the cost value gathered from the
# network data.
TRAIN_COST = TRAIN_CO * ( GA == 0 )
# For numerical reasons, it is good practice to scale the data to
# that the values of the parameters are around 1.0.
# A previous estimation with the unscaled data has generated
# parameters around -0.01 for both cost and time. Therefore, time and
# cost are multipled my 0.01.
# The following statements are designed to preprocess the data. It is
# like creating a new columns in the data file. This should be
# preferred to the statement like
# TRAIN_TT_SCALED = TRAIN_TT / 100.0
# which will cause the division to be reevaluated again and again,
# throuh the iterations. For models taking a long time to estimate, it
# may make a significant difference.
TRAIN_TT_SCALED = DefineVariable('TRAIN_TT_SCALED', TRAIN_TT / 100.0)
TRAIN_COST_SCALED = DefineVariable('TRAIN_COST_SCALED', TRAIN_COST / 100)
CAR_TT_SCALED = DefineVariable('CAR_TT_SCALED', CAR_TT / 100)
CAR_CO_SCALED = DefineVariable('CAR_CO_SCALED', CAR_CO / 100)
V1 = ASC_TRAIN + B_TIME * TRAIN_TT_SCALED + B_COST * TRAIN_COST_SCALED
V3 = ASC_CAR + B_TIME * CAR_TT_SCALED + B_COST * CAR_CO_SCALED #
# Associate choice probability with the numbering of alternatives
P = {1: bioNormalCdf(V1-V3),
3: bioNormalCdf(V3-V1)}
# Associate the availability conditions with the alternatives
CAR_AV_SP = DefineVariable('CAR_AV_SP',CAR_AV * ( SP != 0 ))
TRAIN_AV_SP = DefineVariable('TRAIN_AV_SP',TRAIN_AV * ( SP != 0 ))
av = {1: TRAIN_AV_SP,
3: CAR_AV_SP}
prob = Elem(P,CHOICE)
# Defines an itertor on the data
rowIterator('obsIter')
# DEfine the likelihood function for the estimation
BIOGEME_OBJECT.ESTIMATE = Sum(log(prob),'obsIter')
# All observations verifying the following expression will not be
# considered for estimation
# The modeler here has developed the model only for work trips.
# Observations such that the dependent variable CHOICE is 0 are also removed.
exclude = (TRAIN_AV_SP == 0) + (CAR_AV_SP == 0) + ( CHOICE == 2 ) + (( PURPOSE != 1 ) * ( PURPOSE != 3 ) + ( CHOICE == 0 )) > 0
BIOGEME_OBJECT.EXCLUDE = exclude
# Statistics
nullLoglikelihood(av,'obsIter')
choiceSet = [1,3]
cteLoglikelihood(choiceSet,CHOICE,'obsIter')
availabilityStatistics(av,'obsIter')
BIOGEME_OBJECT.FORMULAS['Train utility'] = V1
BIOGEME_OBJECT.FORMULAS['Car utility'] = V3