LinearExpression

(class from pyomo.core.expr.numeric_expr)

class pyomo.core.expr.numeric_expr.LinearExpression(args=None, constant=None, linear_coefs=None, linear_vars=None)

Bases: SumExpression

An expression object for linear polynomials.

This is a derived :py:class`SumExpression` that guarantees all arguments are one of the following types:

• not potentially variable (e.g., native types, Params, or NPV expressions)

• MonomialTermExpression

• VarData

Parameters:

args (tuple) – Children nodes

__init__(args=None, constant=None, linear_coefs=None, linear_vars=None)

A linear expression of the form const + sum_i(c_i*x_i).

You can specify args OR (constant, linear_coefs, and linear_vars). If args is provided, it should be a list that contains only constants, NPV objects/expressions, variables, or MonomialTermExpression objects. Alternatively, you can specify the constant, the list of linear_coefs and the list of linear_vars separately. Note that these lists are NOT preserved.

Methods

__init__([args, constant, linear_coefs, ...])	A linear expression of the form const + sum_i(c_i*x_i).
add(new_arg)	DEPRECATED.
arg(i)	Return the i-th child node.
clone([substitute])	Return a clone of the expression tree.
create_node_with_local_data(args[, classtype])	Construct a node using given arguments.
create_potentially_variable_object()	DEPRECATED.
getname(*args, **kwds)	Return the text name of a function associated with this expression object.
is_component_type()	Return True if this class is a Pyomo component
is_constant()	Return True if this expression is an atomic constant
is_expression_type([expression_system])	Return True if this object is an expression.
is_fixed()	Return True if this expression contains no free variables.
is_indexed()	Return True if this numeric value is an indexed object
is_logical_type()	Return True if this class is a Pyomo Boolean object.
is_named_expression_type()	Return True if this object is a named expression.
is_numeric_type()	Return True if this class is a Pyomo numeric object
is_parameter_type()	Return False unless this class is a parameter object
is_potentially_variable()	Return True if this expression might represent a variable expression.
is_reference()	Return True if this object is a reference.
is_relational()	DEPRECATED.
is_variable_type()	Return False unless this class is a variable object
nargs()	Returns the number of child nodes.
polynomial_degree()	Return the polynomial degree of the expression.
size()	Return the number of nodes in the expression tree.
to_string([verbose, labeler, smap, ...])	Return a string representation of the expression tree.

Attributes

PRECEDENCE	Return the associativity of this operator.
args	Return the child nodes
constant
linear_coefs
linear_vars
local_name
name

Member Documentation

add(new_arg)

DEPRECATED.

Deprecated since version 6.6.0: SumExpression.add() is deprecated. Please use regular Python operators (infix ‘+’ or inplace ‘+=’.)

arg(i)

Return the i-th child node.

Parameters:

• i (int) – Index of the child argument to return

• Returns (The i-th child node.)

clone(substitute=None)

Return a clone of the expression tree.

Note

This method does not clone the leaves of the tree, which are numeric constants and variables. It only clones the interior nodes, and expression leaf nodes like _MutableLinearExpression. However, named expressions are treated like leaves, and they are not cloned.

Parameters:

substitute (dict) – a dictionary that maps object ids to clone objects generated earlier during the cloning process.

Returns:

A new expression tree.

create_node_with_local_data(args, classtype=None)

Construct a node using given arguments.

This method provides a consistent interface for constructing a node, which is used in tree visitor scripts. In the simplest case, this returns:

self.__class__(args)

But in general this creates an expression object using local data as well as arguments that represent the child nodes.

Parameters:

args (list) – A list of child nodes for the new expression object

Returns:

A new expression object with the same type as the current class.

create_potentially_variable_object()

DEPRECATED.

Create a potentially variable version of this object.

This method returns an object that is a potentially variable version of the current object. In the simplest case, this simply sets the value of __class__:

self.__class__ = self.__class__.__mro__[1]

Note that this method is allowed to modify the current object and return it. But in some cases it may create a new potentially variable object.

Returns:

An object that is potentially variable.

Deprecated since version 6.4.3: The implicit recasting of a “not potentially variable” expression node to a potentially variable one is no longer supported (this violates the immutability promise for Pyomo5 expression trees).

getname(*args, **kwds)

Return the text name of a function associated with this expression object.

In general, no arguments are passed to this function.

Parameters:

• *arg – a variable length list of arguments

• **kwds – keyword arguments

Returns:

A string name for the function.

is_component_type()

Return True if this class is a Pyomo component

is_constant()

Return True if this expression is an atomic constant

This method contrasts with the is_fixed() method. This method returns True if the expression is an atomic constant, that is it is composed exclusively of constants and immutable parameters. NumericValue objects returning is_constant() == True may be simplified to their numeric value at any point without warning.

Note: This defaults to False, but gets redefined in sub-classes.

is_expression_type(expression_system=None)

Return True if this object is an expression.

This method obviously returns True for this class, but it is included in other classes within Pyomo that are not expressions, which allows for a check for expressions without evaluating the class type.

Returns:

A boolean.

is_fixed()

Return True if this expression contains no free variables.

Returns:

A boolean.

is_indexed()

Return True if this numeric value is an indexed object

is_logical_type()

Return True if this class is a Pyomo Boolean object.

Boolean objects include constants, variables, or logical expressions.

is_named_expression_type()

Return True if this object is a named expression.

This method returns False for this class, and it is included in other classes within Pyomo that are not named expressions, which allows for a check for named expressions without evaluating the class type.

Returns:

A boolean.

is_numeric_type()

Return True if this class is a Pyomo numeric object

is_parameter_type()

Return False unless this class is a parameter object

is_potentially_variable()

Return True if this expression might represent a variable expression.

This method returns True when (a) the expression tree contains one or more variables, or (b) the expression tree contains a named expression. In both cases, the expression cannot be treated as constant since (a) the variables may not be fixed, or (b) the named expressions may be changed at a later time to include non-fixed variables.

Returns:

A boolean. Defaults to True for expressions.

is_reference()

Return True if this object is a reference.

is_relational()

DEPRECATED.

Return True if this numeric value represents a relational expression.

Deprecated since version 6.4.3: is_relational() is deprecated in favor of is_expression_type(ExpressionType.RELATIONAL)

is_variable_type()

Return False unless this class is a variable object

nargs()

Returns the number of child nodes.

Note

Individual expression nodes may use different internal storage schemes, so it is imperative that developers use this method and not assume the existence of a particular attribute!

Returns:

int

Return type:

A nonnegative integer that is the number of child nodes.

polynomial_degree()

Return the polynomial degree of the expression.

Returns:

A non-negative integer that is the polynomial degree if the expression is polynomial, or None otherwise.

size()

Return the number of nodes in the expression tree.

Returns:

A nonnegative integer that is the number of interior and leaf nodes in the expression tree.

to_string(verbose=None, labeler=None, smap=None, compute_values=False)

Return a string representation of the expression tree.

Parameters:

• verbose (bool) – If True, then the string representation consists of nested functions. Otherwise, the string representation is an algebraic (infix notation) equation. Defaults to False.

• labeler – An object that generates string labels for variables in the expression tree. Defaults to None.

• smap – If specified, this SymbolMap is used to cache labels for variables.

• (bool) (compute_values) – If True, then parameters and fixed variables are evaluated before the expression string is generated. Default is False.

• Returns – A string representation for the expression tree.

PRECEDENCE = 6

Return the associativity of this operator.

Returns 1 if this operator is left-to-right associative or -1 if it is right-to-left associative. Any other return value will be interpreted as “not associative” (implying any arguments that are at this operator’s PRECEDENCE will be enclosed in parens).

property args

Return the child nodes

Returns:

Sequence containing only the child nodes of this node. The return type depends on the node storage model. Users are not permitted to change the returned data (even for the case of data returned as a list), as that breaks the promise of tree immutability.

Return type:

list or tuple