Variable¶

Variable represents a decision variable in the optimization problem. It can be created by calling the add_variable method of the model:

import pyoptinterface as poi
from pyoptinterface import highs

model = highs.Model()

x = model.add_variable(lb=0, ub=1.0, domain=poi.VariableDomain.Continuous, name="x")

Variable Attributes¶

After a variable is created, we can query or modify its attributes. The following table lists the standard variable attributes:

**Standard variable attributes**¶
Attribute name	Type
Name	str
LowerBound	float
UpperBound	float
Domain	VariableDomain
PrimalStart	float
Value	float

# set the lower bound of the variable
model.set_variable_attribute(x, poi.VariableAttribute.LowerBound, 0.0)
# set the upper bound of the variable
model.set_variable_attribute(x, poi.VariableAttribute.UpperBound, 1.0)

# For mixed-integer programming, we can set the initial value of the variable
model.set_variable_attribute(x, poi.VariableAttribute.PrimalStart, 0.5)

# get the value of the variable after optimization
x_value = model.get_variable_attribute(x, poi.VariableAttribute.Value)

Delete variable¶

We can delete a variable by calling the delete_variable method of the model:

model.delete_variable(x)

After a variable is deleted, it cannot be used in the model anymore, otherwise an exception will be raised.

We can query whether a variable is active by calling the is_variable_active method of the model:

is_active = model.is_variable_active(x)