biogeme.expressions.beta_parameters module

Representation of unknown parameters

author:

Michel Bierlaire

date:

Sat Apr 20 14:54:16 2024

class biogeme.expressions.beta_parameters.Beta(name, value, lowerbound, upperbound, status)[source]

Bases: Elementary

Unknown parameters to be estimated from data.

Parameters:

  • name (str)

  • value (float)

  • lowerbound (float | None)

  • upperbound (float | None)

  • status (int)

change_init_values(betas)[source]

Modifies the initial values of the Beta parameters.

The fact that the parameters are fixed or free is irrelevant here.

Parameters:

betas (dict(string:float)) – dictionary where the keys are the names of the parameters, and the values are the new value for the parameters.

dict_of_elementary_expression(the_type)[source]

Extract a dict with all elementary expressions of a specific type

Parameters:

the_type (TypeOfElementaryExpression) – the type of expression

Returns:

returns a dict with the variables appearing in the expression the keys being their names.

Return type:

dict(string:biogeme.expressions.Expression)

fix_betas(beta_values, prefix=None, suffix=None)[source]

Fix all the values of the Beta parameters appearing in the dictionary

Parameters:

  • beta_values (dict(str: float)) – dictionary containing the betas to be fixed (as key) and their value.

  • prefix (str) – if not None, the parameter is renamed, with a prefix defined by this argument.

  • suffix (str) – if not None, the parameter is renamed, with a suffix defined by this argument.

getValue()[source]

Warning

This function is deprecated. Use get_value() instead.

Kept for backward compatibility

Return type:

float

get_signature()[source]

The signature of a string characterizing an expression.

This is designed to be communicated to C++, so that the expression can be reconstructed in this environment.

The list contains the following elements:

  1. the name of the expression between < >

  2. the id of the expression between { }

  3. the name of the parameter,

  4. the status between [ ]

  5. the unique ID, preceded by a comma

  6. the Beta ID, preceded by a comma

Consider the following expression:

\[2 \beta_1 V_1 - \frac{\exp(-\beta_2 V_2) }{ \beta_3 (\beta_2 \geq \beta_1)}.\]

It is defined as:

2 * beta1 * Variable1 - expressions.exp(-beta2*Variable2) /
     (beta3 * (beta2 >= beta1))

And its signature is:

[b'<Numeric>{4780527008},2',
 b'<Beta>{4780277152}"beta1"[0],0,0',
 b'<Times>{4780526952}(2),4780527008,4780277152',
 b'<Variable>{4511837152}"Variable1",5,2',
 b'<Times>{4780527064}(2),4780526952,4511837152',
 b'<Beta>{4780277656}"beta2"[0],1,1',
 b'<UnaryMinus>{4780527120}(1),4780277656',
 b'<Variable>{4511837712}"Variable2",6,3',
 b'<Times>{4780527176}(2),4780527120,4511837712',
 b'<exp>{4780527232}(1),4780527176',
 b'<Beta>{4780277264}"beta3"[1],2,0',
 b'<Beta>{4780277656}"beta2"[0],1,1',
 b'<Beta>{4780277152}"beta1"[0],0,0',
 b'<GreaterOrEqual>{4780527288}(2),4780277656,4780277152',
 b'<Times>{4780527344}(2),4780277264,4780527288',
 b'<Divide>{4780527400}(2),4780527232,4780527344',
 b'<Minus>{4780527456}(2),4780527064,4780527400']
Returns:

list of the signatures of an expression and its children.

Return type:

list(string)

Raises:

  • BiogemeError – if no id has been defined for elementary expression

  • BiogemeError – if no id has been defined for parameter

get_value()[source]

Evaluates the value of the expression

Returns:

value of the expression

Return type:

float

Raises:

BiogemeError – if the Beta is not fixed.

set_id_manager(id_manager)[source]

The ID manager contains the IDs of the elementary expressions.

It is externally created, as it may need to coordinate the numbering of several expressions. It is stored only in the expressions of type Elementary.

Parameters:

id_manager (class IdManager) – ID manager to be propagated to the elementary expressions. If None, all the IDs are set to None.