Core Classes

The following are the two core classes documented here:

• NumericValue

• NumericExpression

The remaining classes are the public classes for expressions, which developers may need to know about. The methods for these classes are not documented because they are described in the NumericExpression class.

Sets with Expression Types

The following sets can be used to develop visitor patterns for Pyomo expressions.

pyomo.core.expr.numvalue.native_numeric_types = {<class 'numpy.int16'>, <class 'float'>, <class 'numpy.float64'>, <class 'numpy.uint32'>, <class 'numpy.int32'>, <class 'complex'>, <class 'numpy.uint64'>, <class 'int'>, <class 'numpy.int64'>, <class 'numpy.float16'>, <class 'numpy.uint8'>, <class 'numpy.int8'>, <class 'numpy.float32'>, <class 'numpy.uint16'>}

set() -> new empty set object set(iterable) -> new set object

Build an unordered collection of unique elements.

pyomo.core.expr.numvalue.native_types = {<class 'numpy.uint64'>, <class 'numpy.int64'>, <class 'str'>, <class 'numpy.float64'>, <class 'numpy.uint32'>, <class 'numpy.int32'>, <class 'NoneType'>, <class 'slice'>, <class 'numpy.float32'>, <class 'numpy.uint16'>, <class 'numpy.int16'>, <class 'numpy.bool_'>, <class 'complex'>, <class 'bytes'>, <class 'numpy.ndarray'>, <class 'numpy.float16'>, <class 'numpy.uint8'>, <class 'numpy.int8'>, <class 'bool'>, <class 'float'>, <class 'int'>}

set() -> new empty set object set(iterable) -> new set object

Build an unordered collection of unique elements.

pyomo.core.expr.numvalue.nonpyomo_leaf_types = {<class 'numpy.uint64'>, <class 'numpy.int64'>, <class 'str'>, <class 'numpy.float64'>, <class 'numpy.uint32'>, <class 'numpy.int32'>, <class 'NoneType'>, <class 'slice'>, <class 'numpy.float32'>, <class 'numpy.uint16'>, <class 'numpy.int16'>, <class 'numpy.bool_'>, <class 'complex'>, <class 'pyomo.core.expr.numvalue.NonNumericValue'>, <class 'bytes'>, <class 'numpy.float16'>, <class 'numpy.uint8'>, <class 'numpy.int8'>, <class 'bool'>, <class 'float'>, <class 'int'>}

set() -> new empty set object set(iterable) -> new set object

Build an unordered collection of unique elements.

NumericValue and NumericExpression

class pyomo.core.expr.numvalue.NumericValue

This is the base class for numeric values used in Pyomo.

__abs__()

Absolute value

This method is called when Python processes the statement:

abs(self)

__add__(other)

Binary addition

This method is called when Python processes the statement:

self + other

__bool__()

Coerce the value to a bool

Numeric values can be coerced to bool only if the value / expression is constant. Fixed (but non-constant) or variable values will raise an exception.

Raises:

PyomoException –

__div__(other)

Binary division

This method is called when Python processes the statement:

self / other

__eq__(other)

Equal to operator

This method is called when Python processes the statement:

self == other

__float__()

Coerce the value to a floating point

Numeric values can be coerced to float only if the value / expression is constant. Fixed (but non-constant) or variable values will raise an exception.

Raises:

TypeError –

__ge__(other)

Greater than or equal operator

This method is called when Python processes statements of the form:

self >= other
other <= self

__gt__(other)

Greater than operator

This method is called when Python processes statements of the form:

self > other
other < self

__hash__ = None

__iadd__(other)

Binary addition

This method is called when Python processes the statement:

self += other

__idiv__(other)

Binary division

This method is called when Python processes the statement:

self /= other

__imul__(other)

Binary multiplication

This method is called when Python processes the statement:

self *= other

__int__()

Coerce the value to an integer

Numeric values can be coerced to int only if the value / expression is constant. Fixed (but non-constant) or variable values will raise an exception.

Raises:

TypeError –

__ipow__(other)

Binary power

This method is called when Python processes the statement:

self **= other

__isub__(other)

Binary subtraction

This method is called when Python processes the statement:

self -= other

__itruediv__(other)

Binary division (when __future__.division is in effect)

This method is called when Python processes the statement:

self /= other

__le__(other)

Less than or equal operator

This method is called when Python processes statements of the form:

self <= other
other >= self

__lt__(other)

Less than operator

This method is called when Python processes statements of the form:

self < other
other > self

__mul__(other)

Binary multiplication

This method is called when Python processes the statement:

self * other

__neg__()

Negation

This method is called when Python processes the statement:

- self

__pos__()

Positive expression

This method is called when Python processes the statement:

+ self

__pow__(other)

Binary power

This method is called when Python processes the statement:

self ** other

__radd__(other)

Binary addition

This method is called when Python processes the statement:

other + self

__rdiv__(other)

Binary division

This method is called when Python processes the statement:

other / self

__rmul__(other)

Binary multiplication

This method is called when Python processes the statement:

other * self

when other is not a NumericValue object.

__rpow__(other)

Binary power

This method is called when Python processes the statement:

other ** self

__rsub__(other)

Binary subtraction

This method is called when Python processes the statement:

other - self

__rtruediv__(other)

Binary division (when __future__.division is in effect)

This method is called when Python processes the statement:

other / self

__sub__(other)

Binary subtraction

This method is called when Python processes the statement:

self - other

__truediv__(other)

Binary division (when __future__.division is in effect)

This method is called when Python processes the statement:

self / other

_compute_polynomial_degree(values)

Compute the polynomial degree of this expression given the degree values of its children.

Parameters:

values (list) – A list of values that indicate the degree of the children expression.

Returns:

None

getname(fully_qualified=False, name_buffer=None)

If this is a component, return the component’s name on the owning block; otherwise return the value converted to a string

is_constant()

Return True if this numeric value is a constant value

is_fixed()

Return True if this is a non-constant value that has been fixed

is_indexed()

Return True if this numeric value is an indexed object

is_numeric_type()

Return True if this class is a Pyomo numeric object

is_potentially_variable()

Return True if variables can appear in this expression

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)

polynomial_degree()

Return the polynomial degree of the expression.

Returns:

None

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 infix algebraic equation. Defaults to False.

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

• smap – A SymbolMap instance that stores string labels for non-constant nodes in the expression tree. Defaults to None.

• compute_values (bool) – If True, then fixed expressions are evaluated and the string representation of the resulting value is returned.

Returns:

A string representation for the expression tree.

class pyomo.core.expr.NumericExpression(args)

Bases: ExpressionBase, NumericValue

The base class for Pyomo expressions.

This class is used to define nodes in a numeric expression tree.

Parameters:

args (list or tuple) – Children of this node.

PRECEDENCE = 0

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).

__init__(args)

_compute_polynomial_degree(values)

Compute the polynomial degree of this expression given the degree values of its children.

This method is called by the _PolynomialDegreeVisitor class. It can be over-written by expression classes to customize this logic.

Parameters:

values (list) – A list of values that indicate the degree of the children expression.

Returns:

A nonnegative integer that is the polynomial degree of the expression, or None. Default is None.

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

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 that immutability promise for Pyomo5 expression trees).

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.

Other Public Classes

class pyomo.core.expr.NegationExpression(args)

Bases: NumericExpression

Negation expressions:

- x

PRECEDENCE = 4

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).

_apply_operation(result)

Compute the values of this node given the values of its children.

This method is called by the _EvaluationVisitor class. It must be over-written by expression classes to customize this logic.

Note

This method applies the logical operation of the operator to the arguments. It does not evaluate the arguments in the process, but assumes that they have been previously evaluated. But note that if this class contains auxiliary data (e.g. like the numeric coefficients in the LinearExpression class) then those values must be evaluated as part of this function call. An uninitialized parameter value encountered during the execution of this method is considered an error.

Parameters:

values (list) – A list of values that indicate the value of the children expressions.

Returns:

A floating point value for this expression.

_compute_polynomial_degree(result)

Compute the polynomial degree of this expression given the degree values of its children.

This method is called by the _PolynomialDegreeVisitor class. It can be over-written by expression classes to customize this logic.

Parameters:

values (list) – A list of values that indicate the degree of the children expression.

Returns:

A nonnegative integer that is the polynomial degree of the expression, or None. Default is None.

_to_string(values, verbose, smap)

Construct a string representation for this node, using the string representations of its children.

This method is called by the _ToStringVisitor class. It must must be defined in subclasses.

Parameters:

• values (list) – The string representations of the children of this node.

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

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

Returns:

A string representation for this node.

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.

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.

class pyomo.core.expr.ExternalFunctionExpression(args, fcn=None)

Bases: NumericExpression

External function expressions

Example:

model = ConcreteModel()
model.a = Var()
model.f = ExternalFunction(library='foo.so', function='bar')
expr = model.f(model.a)

Parameters:

• args (tuple) – children of this node

• fcn – a class that defines this external function

PRECEDENCE = None

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).

_apply_operation(result)

Compute the values of this node given the values of its children.

This method is called by the _EvaluationVisitor class. It must be over-written by expression classes to customize this logic.

Note

This method applies the logical operation of the operator to the arguments. It does not evaluate the arguments in the process, but assumes that they have been previously evaluated. But note that if this class contains auxiliary data (e.g. like the numeric coefficients in the LinearExpression class) then those values must be evaluated as part of this function call. An uninitialized parameter value encountered during the execution of this method is considered an error.

Parameters:

values (list) – A list of values that indicate the value of the children expressions.

Returns:

A floating point value for this expression.

_fcn

_to_string(values, verbose, smap)

Construct a string representation for this node, using the string representations of its children.

This method is called by the _ToStringVisitor class. It must must be defined in subclasses.

Parameters:

• values (list) – The string representations of the children of this node.

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

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

Returns:

A string representation for this node.

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.

get_arg_units()

Return the units for this external functions arguments

get_units()

Get the units of the return value for this external function

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.

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.

class pyomo.core.expr.ProductExpression(args)

Bases: NumericExpression

Product expressions:

x*y

PRECEDENCE = 4

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).

_apply_operation(result)

Compute the values of this node given the values of its children.

This method is called by the _EvaluationVisitor class. It must be over-written by expression classes to customize this logic.

Note

This method applies the logical operation of the operator to the arguments. It does not evaluate the arguments in the process, but assumes that they have been previously evaluated. But note that if this class contains auxiliary data (e.g. like the numeric coefficients in the LinearExpression class) then those values must be evaluated as part of this function call. An uninitialized parameter value encountered during the execution of this method is considered an error.

Parameters:

values (list) – A list of values that indicate the value of the children expressions.

Returns:

A floating point value for this expression.

_compute_polynomial_degree(result)

Compute the polynomial degree of this expression given the degree values of its children.

This method is called by the _PolynomialDegreeVisitor class. It can be over-written by expression classes to customize this logic.

Parameters:

values (list) – A list of values that indicate the degree of the children expression.

Returns:

A nonnegative integer that is the polynomial degree of the expression, or None. Default is None.

_is_fixed(args)

Compute whether this expression is fixed given the fixed values of its children.

This method is called by the _IsFixedVisitor class. It can be over-written by expression classes to customize this logic.

Parameters:

values (list) – A list of boolean values that indicate whether the children of this expression are fixed

Returns:

A boolean that is True if the fixed values of the children are all True.

_to_string(values, verbose, smap)

Construct a string representation for this node, using the string representations of its children.

This method is called by the _ToStringVisitor class. It must must be defined in subclasses.

Parameters:

• values (list) – The string representations of the children of this node.

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

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

Returns:

A string representation for this node.

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.

class pyomo.core.expr.DivisionExpression(args)

Bases: NumericExpression

Division expressions:

x/y

PRECEDENCE = 4

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).

_apply_operation(result)

Compute the values of this node given the values of its children.

This method is called by the _EvaluationVisitor class. It must be over-written by expression classes to customize this logic.

Note

This method applies the logical operation of the operator to the arguments. It does not evaluate the arguments in the process, but assumes that they have been previously evaluated. But note that if this class contains auxiliary data (e.g. like the numeric coefficients in the LinearExpression class) then those values must be evaluated as part of this function call. An uninitialized parameter value encountered during the execution of this method is considered an error.

Parameters:

values (list) – A list of values that indicate the value of the children expressions.

Returns:

A floating point value for this expression.

_compute_polynomial_degree(result)

Compute the polynomial degree of this expression given the degree values of its children.

This method is called by the _PolynomialDegreeVisitor class. It can be over-written by expression classes to customize this logic.

Parameters:

values (list) – A list of values that indicate the degree of the children expression.

Returns:

A nonnegative integer that is the polynomial degree of the expression, or None. Default is None.

_to_string(values, verbose, smap)

Construct a string representation for this node, using the string representations of its children.

This method is called by the _ToStringVisitor class. It must must be defined in subclasses.

Parameters:

• values (list) – The string representations of the children of this node.

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

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

Returns:

A string representation for this node.

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.

class pyomo.core.expr.InequalityExpression(args, strict)

Bases: RelationalExpression

Inequality expressions, which define less-than or less-than-or-equal relations:

x < y
x <= y

Parameters:

• args (tuple) – child nodes

• strict (bool) – a flag that indicates whether the inequality is strict

PRECEDENCE = 9

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).

_apply_operation(result)

Compute the values of this node given the values of its children.

This method is called by the _EvaluationVisitor class. It must be over-written by expression classes to customize this logic.

Note

This method applies the logical operation of the operator to the arguments. It does not evaluate the arguments in the process, but assumes that they have been previously evaluated. But note that if this class contains auxiliary data (e.g. like the numeric coefficients in the LinearExpression class) then those values must be evaluated as part of this function call. An uninitialized parameter value encountered during the execution of this method is considered an error.

Parameters:

values (list) – A list of values that indicate the value of the children expressions.

Returns:

A floating point value for this expression.

_strict

_to_string(values, verbose, smap)

Construct a string representation for this node, using the string representations of its children.

This method is called by the _ToStringVisitor class. It must must be defined in subclasses.

Parameters:

• values (list) – The string representations of the children of this node.

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

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

Returns:

A string representation for this node.

create_node_with_local_data(args)

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.

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.

property strict

class pyomo.core.expr.EqualityExpression(args)

Bases: RelationalExpression

Equality expression:

x == y

PRECEDENCE = 9

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).

_apply_operation(result)

Compute the values of this node given the values of its children.

This method is called by the _EvaluationVisitor class. It must be over-written by expression classes to customize this logic.

Note

This method applies the logical operation of the operator to the arguments. It does not evaluate the arguments in the process, but assumes that they have been previously evaluated. But note that if this class contains auxiliary data (e.g. like the numeric coefficients in the LinearExpression class) then those values must be evaluated as part of this function call. An uninitialized parameter value encountered during the execution of this method is considered an error.

Parameters:

values (list) – A list of values that indicate the value of the children expressions.

Returns:

A floating point value for this expression.

_to_string(values, verbose, smap)

Construct a string representation for this node, using the string representations of its children.

This method is called by the _ToStringVisitor class. It must must be defined in subclasses.

Parameters:

• values (list) – The string representations of the children of this node.

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

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

Returns:

A string representation for this node.

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.

class pyomo.core.expr.SumExpression(args)

Bases: NumericExpression

Sum expression:

x + y + ...

This node represents an “n-ary” sum expression over at least 2 arguments.

Parameters:

args (list) – Children nodes

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).

_apply_operation(result)

Compute the values of this node given the values of its children.

This method is called by the _EvaluationVisitor class. It must be over-written by expression classes to customize this logic.

Note

This method applies the logical operation of the operator to the arguments. It does not evaluate the arguments in the process, but assumes that they have been previously evaluated. But note that if this class contains auxiliary data (e.g. like the numeric coefficients in the LinearExpression class) then those values must be evaluated as part of this function call. An uninitialized parameter value encountered during the execution of this method is considered an error.

Parameters:

values (list) – A list of values that indicate the value of the children expressions.

Returns:

A floating point value for this expression.

_compute_polynomial_degree(result)

Compute the polynomial degree of this expression given the degree values of its children.

This method is called by the _PolynomialDegreeVisitor class. It can be over-written by expression classes to customize this logic.

Parameters:

values (list) – A list of values that indicate the degree of the children expression.

Returns:

A nonnegative integer that is the polynomial degree of the expression, or None. Default is None.

_nargs

_to_string(values, verbose, smap)

Construct a string representation for this node, using the string representations of its children.

This method is called by the _ToStringVisitor class. It must must be defined in subclasses.

Parameters:

• values (list) – The string representations of the children of this node.

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

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

Returns:

A string representation for this node.

add(new_arg)

DEPRECATED.

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

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

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.

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.

class pyomo.core.expr.GetItemExpression(args=())

Bases: ExpressionBase

Expression to call __getitem__() on the base object.

PRECEDENCE = 1

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).

_apply_operation(result)

Compute the values of this node given the values of its children.

This method is called by the _EvaluationVisitor class. It must be over-written by expression classes to customize this logic.

Note

This method applies the logical operation of the operator to the arguments. It does not evaluate the arguments in the process, but assumes that they have been previously evaluated. But note that if this class contains auxiliary data (e.g. like the numeric coefficients in the LinearExpression class) then those values must be evaluated as part of this function call. An uninitialized parameter value encountered during the execution of this method is considered an error.

Parameters:

values (list) – A list of values that indicate the value of the children expressions.

Returns:

A floating point value for this expression.

_is_fixed(values)

Compute whether this expression is fixed given the fixed values of its children.

This method is called by the _IsFixedVisitor class. It can be over-written by expression classes to customize this logic.

Parameters:

values (list) – A list of boolean values that indicate whether the children of this expression are fixed

Returns:

A boolean that is True if the fixed values of the children are all True.

_resolve_template(args)

_to_string(values, verbose, smap)

Construct a string representation for this node, using the string representations of its children.

This method is called by the _ToStringVisitor class. It must must be defined in subclasses.

Parameters:

• values (list) – The string representations of the children of this node.

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

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

Returns:

A string representation for this node.

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.

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.

class pyomo.core.expr.Expr_ifExpression(args)

Bases: NumericExpression

A numeric ternary (if-then-else) expression:

Expr_if(IF=x, THEN=y, ELSE=z)

Note that this is a mixed expression: IF can be numeric or logical; THEN and ELSE are numeric, and the result is a numeric expression.

PRECEDENCE = None

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).

_apply_operation(result)

Compute the values of this node given the values of its children.

This method is called by the _EvaluationVisitor class. It must be over-written by expression classes to customize this logic.

Note

This method applies the logical operation of the operator to the arguments. It does not evaluate the arguments in the process, but assumes that they have been previously evaluated. But note that if this class contains auxiliary data (e.g. like the numeric coefficients in the LinearExpression class) then those values must be evaluated as part of this function call. An uninitialized parameter value encountered during the execution of this method is considered an error.

Parameters:

values (list) – A list of values that indicate the value of the children expressions.

Returns:

A floating point value for this expression.

_compute_polynomial_degree(result)

Compute the polynomial degree of this expression given the degree values of its children.

This method is called by the _PolynomialDegreeVisitor class. It can be over-written by expression classes to customize this logic.

Parameters:

values (list) – A list of values that indicate the degree of the children expression.

Returns:

A nonnegative integer that is the polynomial degree of the expression, or None. Default is None.

_is_fixed(args)

Compute whether this expression is fixed given the fixed values of its children.

This method is called by the _IsFixedVisitor class. It can be over-written by expression classes to customize this logic.

Parameters:

values (list) – A list of boolean values that indicate whether the children of this expression are fixed

Returns:

A boolean that is True if the fixed values of the children are all True.

_to_string(values, verbose, smap)

Construct a string representation for this node, using the string representations of its children.

This method is called by the _ToStringVisitor class. It must must be defined in subclasses.

Parameters:

• values (list) – The string representations of the children of this node.

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

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

Returns:

A string representation for this node.

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.

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.

class pyomo.core.expr.UnaryFunctionExpression(args, name=None, fcn=None)

Bases: NumericExpression

An expression object for intrinsic (math) functions (e.g. sin, cos, tan).

Parameters:

• args (tuple) – Children nodes

• name (string) – The function name

• fcn – The function that is used to evaluate this expression

PRECEDENCE = None

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).

_apply_operation(result)

Compute the values of this node given the values of its children.

This method is called by the _EvaluationVisitor class. It must be over-written by expression classes to customize this logic.

Note

This method applies the logical operation of the operator to the arguments. It does not evaluate the arguments in the process, but assumes that they have been previously evaluated. But note that if this class contains auxiliary data (e.g. like the numeric coefficients in the LinearExpression class) then those values must be evaluated as part of this function call. An uninitialized parameter value encountered during the execution of this method is considered an error.

Parameters:

values (list) – A list of values that indicate the value of the children expressions.

Returns:

A floating point value for this expression.

_fcn

_name

_to_string(values, verbose, smap)

Construct a string representation for this node, using the string representations of its children.

This method is called by the _ToStringVisitor class. It must must be defined in subclasses.

Parameters:

• values (list) – The string representations of the children of this node.

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

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

Returns:

A string representation for this node.

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.

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.

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.

class pyomo.core.expr.AbsExpression(arg)

Bases: UnaryFunctionExpression

An expression object for the abs() function.

Parameters:

args (tuple) – Children nodes

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.