8.6.17. LinExpr¶

class LinExpr¶

Represents a linear expression. Usually related to constraints or objective functions. A linear expression contains many linear terms and a constant term. Linear expressions can be involved in arithmetic operations. For example:

# constant term increased by 1
linExpr += 1
linExpr = linExpr +1
# add a linear term
linExpr += x
-linExpr
# a MLinExpr
linExpr + numpy.ones((2, 2))
# a QuadExpr
linExpr * x
# a MQuadExpr
linexpr * mLinExpr

Methods

`__init__()`	Construct a linear expression
`add()`	Add all terms of another linear expression to the current linear expression
`addConstant()`	Add a value to the constant term of the linear expression
`addTerms()`	Add one or more term(s)
`clear()`	Clear all included terms and set constant to 0
`getCoeff()`	Obtain the coefficient of a term in a linear expression
`getConstant()`	Obtain the constant term of a linear expression
`getValue()`	After solving the problem, obtain the value of the linear expression
`getVar()`	Get the variable of a term in a linear expression
`remove()`	Delete some terms contained in an expression
`size()`	Obtain the number of terms, excluding constant terms

__init__(arg1=0, arg2=None)¶

Construct a linear expression

Parameters

arg1=0 – When two parameters are provided during a call, arg1 is usually a coefficient or a list of coefficients.
arg2=None – When two parameters are provided during a call, arg2 is usually a variable or a list of variables.

example:

LinExpr((1, 2, 3), (x, y, z))
LinExpr(2, y)
LinExpr(x)
LinExpr(2 * x + 1)
LinExpr(1)

add(expr, mult=1.0)¶

Add all terms of another linear expression to the current linear expression

Parameters

expr – Another linear expression
mult=1.0 – Multiplier. Default value: 1.0.

example:

linExpr.add(expr, -1)

addConstant(c)¶

Add a value to the constant term of the linear expression

Parameters: c – The value to be added. A negative number indicates that value should be subtracted.

example:

linExpr.addConstant(-linExpr.getConstant())

addTerms(coeffs, vars)¶

Add one or more term(s)

Parameters

coeffs – The coefficient of the term(s) to be added, which may be a number or an array.
vars – The variable of the term(s) to be added, which can be a single variable or an array.

example:

linExpr.addTerms([1, 2], [x, y])
linExpr.addTerms(1, x)

clear()¶

Clear all included terms and set constant to 0

example:

linExpr = 2 * x +3 * y +1
linExpr.clear()
print(linExpr.size() == 0)
print(linExpr.getConstant() == 0)

getCoeff(index)¶

Obtain the coefficient of a term in a linear expression.

Parameters: index – The index of the term to obtain the coefficient.

example:

linExpr = 2 * x + 1 * y
print(linExpr.getCoeff(1) == 1.0)

getConstant()¶

Obtain the constant term of a linear expression.

example:

linExpr.addConstant(-linExpr.getConstant())

getValue()¶

After solving the problem, obtain the value of the linear expression

example:

m.optimize()
linExpr = 2 * x + y * 1
print(linExpr.getValue())

getVar(index)¶

Get the variable of a term in a linear expression

Parameters: index – The index of the term to obtain the variable from

example:

linExpr = 2 * x + 1 * y
print(linExpr.getVar(1).sameAs(y))

remove(item)¶

Delete some terms contained in an expression

Parameters: item – If item is a number, the term whose index is item is deleted. If item is a variable, all terms that contain this variable are deleted.

example:

linExpr = 2 * x +3 * y +4 * x
linExpr.remove(1)
linExpr.remove(x)
print(linExpr.size() == 0)

size()¶

Obtain the number of terms, excluding constant terms.

example:

linExpr = 2 * x +3 * y +1
print(linExpr.size() == 2)