XPRBexpr

Composing expressions from other quadratic and linear expressions ( expr), variables ( var) and double values ( val). The following operators are defined:

- var

- expr

expr1 + expr2

expr1 - expr2

expr * val

val * expr

var * val

val * var

var * val

var * expr

Throws exception `Non-quadratic expression' if the result of the operation is not quadratic

expr * var

Throws exception `Non-quadratic expression' if the result of the operation is not quadratic

expr1 * expr2

Throws exception `Non-quadratic expression' if the result of the operation is not quadratic

Functions outside any class definition that generate quadratic expressions:

XPRBexpr sqr(XPRBexpr& e);
XPRBexpr sqr(XPRBvar& var);

Square of an expression or variable.

Constructor detail

XPRBexpr

Synopsis

XPRBexpr(double d);
XPRBexpr(int i);
XPRBexpr(double d, XPRBvar& v);
XPRBexpr(double d, XPRBvar& v, XPRBvar& v2);
XPRBexpr(XPRBvar& v);
XPRBexpr(XPRBexpr& e);

Arguments

d	A real value.
i	An integer value.
v,v2	BCL variables (may be the same).
e	A linear or quadratic expression.

Description

Create a new expression.

Method detail

add

Synopsis

XPRBexpr& add(XPRBexpr& e);
XPRBexpr& add(XPRBvar& v);

Arguments

e	A linear or quadratic expression (may be just a constant).
v	A BCL variable.

Return value

The modified expression.

Description

This method adds an expression / constant / variable to the linear or quadratic expression it is applied to.

Example

See XPRBexpr.setTerm.

addTerm

Synopsis

Arguments

var,var2	BCL decision variables (may be the same).
val	A real value (coefficient).

Return value

The modified expression.

Description

This method adds a new term to an expression comprising the variable var (or the product of variables var and var2) with coefficient val. If the expression already has a term with variable var (respectively variables var and var2), val is added to its coefficient. If no variable is specified, the value val is added to the constant term of the expression. Terms can also be added with method XPRBexpr.add.

Example

See XPRBexpr.setTerm.

assign

Synopsis

XPRBexpr& assign(XPRBexpr& e);

Argument

e	Expression to be copied.

Return value

Copy of the expression in the argument.

Description

This method copies the given expression.

delTerm

Synopsis

int delTerm(XPRBvar& var);
int delTerm(XPRBvar& var, XPRBvar& var2);

Argument

var,var2

BCL decision variables (may be the same).

Return value

The modified expression.

Description

This function deletes a variable term from an expression. The constant term is changed or reset with method XPRBexpr.setTerm.

Example

See XPRBexpr.setTerm.

getSol

Synopsis

double getSol();

Return value

Evaluation of the expression with the last solution.

Description

This method returns the evaluation of an expression with the solution values from the last solution found. If this method is called after completion of a branch and bound tree search and an integer solution has been found (that is, if method XPRBprob.getMIPStat returns values XPRB_MIP_SOLUTION or XPRB_MIP_OPTIMAL), it returns the value corresponding to the best integer solution. If no integer solution is available after a branch and bound tree search this method outputs a warning and returns 0. In all other cases it returns the evaluation corresponding to the last LP that has been solved. If this method is used during the execution of an optimization process (for instance in Optimizer library callback functions) it needs to be preceded by a call to XPRBprob.sync with the flag XPRB_XPRS_SOL.

mul

Synopsis

XPRBexpr& mul(double d);
XPRBexpr& mul(XPRBexpr& e);

Arguments

d	A constant.
e	An expression (may be just a constant or a single decision variable).

Return value

The modified expression.

Error handling

ArithmeticException `Non-quadratic expression' if the result of the operation is not quadratic.

Description

This method multiplies an expression by a constant factor or another expression. This operation succeeds if one of the expressions is just a constant or if both expressions have only linear terms.

Example

See XPRBexpr.setTerm.

neg

Synopsis

XPRBexpr& neg();

Return value

Negation of the expression.

Description

This method multiplies an expression with -1.

Example

See XPRBexpr.setTerm.

setTerm

Synopsis

Arguments

var,var2	BCL decision variables (may be the same).
val	A real value (coefficient).

Return value

The modified expression.

Description

This method sets the coefficient of a variable or of the product of the two specified variables to the value val. If no variable is specified, the constant term of the expression is set to val.

Example

This example shows different ways of defining and modifying a quadratic expression and finally sets the resulting expression as objective function. The comments display the definition of qe after each modification.

XPRBvar x,y;
XPRBexpr qe;
XPRBprob prob("myprob");

x = prob.newVar("x", XPRB_PL, 0, 200);
y = prob.newVar("y", XPRB_PL, 0, 200);

qe = x;                 //  x
qe.mul(3*x);            //  3*x^2
qe += x*2*y;            //  3*x^2 + 2*x*y
qe.add(1);              //  1 + 3*x^2 + 2*x*y
qe.setTerm(3, x);       //  1 + 3*x + 3*x^2 + 2*x*y
qe.setTerm(0, x, y);    //  1 + 3*x + 3*x^2
qe.delTerm(x, x);       //  1 + 3*x
qe.setTerm(-1);         //  - 1 + 3*x
qe.addTerm(2, x);       //  - 1 + 5*x
qe -= 3*sqr(3*y);       //  - 1 + 5*x - 27*y^2
qe.neg();               //  1 - 5*x + 27*y^2

prob.setObj(qe);

sqr

Synopsis

XPRBexpr sqr(XPRBexpr& e);
XPRBexpr sqr(XPRBvar& var);

Arguments

e	An expression.
var	A BCL decision variable.

Return value

The square of the variable or expression in the argument.

Description

This function returns the square of the variable or expression passed in the argument if the result is at most quadratic.

Example

See XPRBexpr.setTerm.

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