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Expression

  • java.lang.Object
    • com.dashoptimization.objects.Expression
  • Direct Known Subclasses:
    AbstractExpression, Variable 
    public abstract class Expression
extends java.lang.Object
    Base class for all expressions. Expressions are the building blocks for all constraints represented by Inequality and also for indicator constraints. Expressions are created by combining variables and constant using operators and functions. The operators available for combining constants, variables and expressions are plus, minus, mul (multiply) and div (divide) and are defined as member functions of the Expression class (or its subclasses). To add two variables x and y one would do ce. x.plus(y). To create the expression 2x + 3y one could write x.mul(2).plus(y.mul(3)). The functions that can be used to combine expressions can be found in the Utils class. Examples are sum, sin, etc. Expressions are unmodifiable and are represented as expression trees. This means that all operators are implemented to take only constant time to produce the result. An exception to the above are linear and quadratic expressions (class LinExpression and QuadExpression). Linear and quadratic expressions are very common to math programming and thus they can be built in even more efficient ways: The LinExpression and QuadExpression are the only mutable expressions. They can be modified using the addTerm() family of functions. When creating a linear expression like 2x+3y+4z then it is more efficient to do this as LinExpression.create().addTerm(x,2).addTerm(y,3).addTerm(z,4) than to create the expression using operators plus and mul. For short expressions the performance difference will not be measurable but for longer expressions it will start to matter. Since operators copy their argument expressions by reference, care must be taken when applying operators to LinExpression or QuadExpression: when changing an instance of LinExpression or QuadExpression, this will implicitly change any other expression that references this expression through operators or functions.
    Since:
    43.00

    • Constructor Summary

      Constructor Description
      Expression()  

    • Method Summary

      Modifier and Type Method Description
      Expression div​(double arg)
      Create a new expression that represents the quotient of this and arg.
      Expression div​(Expression arg)
      Create a new expression that represents the quotient of this and arg.
      abstract Inequality.Definition eq​(double rhs)
      Create an "equals" constraint with this expression as left-hand side.
      abstract Inequality.Definition eq​(Expression rhs)
      Create an "equals" constraint with this expression as left-hand side.
      abstract double evaluate​(double[] solution)
      Compute the value of this expression with respect to the given solution vector (which is not required to be feasible).
      abstract void extract​(double factor, PostfixExtractor extractor)
      Extract this expression into postfix notation.
      abstract boolean extract​(double factor, XPRSprob.RowCreator creator)
      Extract this expression into a row.
      abstract Inequality.Definition geq​(double rhs)
      Create a "greater than or equal" constraint with this expression as left-hand side.
      abstract Inequality.Definition geq​(Expression rhs)
      Create a "greater than or equal" constraint with this expression as left-hand side.
      abstract double getConstantView()
      Get the constant value to which this expression evaluates.
      abstract LinearView getLinearView()
      Get a linear read-only view on this expression.
      abstract int getMaxDegree()
      Get the maximum degree of any of the terms/monomials that appear in the symbolic representation of all parenthesized sub-expressions are fully expanded.
      abstract QuadView getQuadView()
      Get a quadratic read-only view on this expression.
      abstract Inequality.Definition in​(double lb, double ub)
      Create a range constraint that bounds this expression from below and above.
      abstract Inequality.Definition leq​(double rhs)
      Create a "less than or equal" constraint with this expression as left-hand side.
      abstract Inequality.Definition leq​(Expression rhs)
      Create a "less than or equal" constraint with this expression as left-hand side.
      Expression minus​(double arg)
      Create a new expression that represents the difference of this and arg.
      Expression minus​(Expression arg)
      Create a new expression that represents the difference of this and arg.
      Expression mul​(double arg)
      Create a new expression that represents the product of this and arg.
      Expression mul​(Expression arg)
      Create a new expression that represents the product of this and arg.
      Expression plus​(double arg)
      Create a new expression that represents the sum of this and arg.
      Expression plus​(Expression arg)
      Create a new expression that represents the sum of this and arg.
      Expression uminus()
      Create a new expression that represents the unary minus of this one.

      • Methods inherited from class java.lang.Object

        equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Constructor Detail

      • Expression

        public Expression()

    • Method Detail

      • leq

        public abstract Inequality.Definition leq​(double rhs)
        Create a "less than or equal" constraint with this expression as left-hand side.
        Parameters:
        rhs - Right-hand side of new constraint.
        Returns:
        The new constraint.
        Since:
        43.00

      • leq

        public abstract Inequality.Definition leq​(Expression rhs)
        Create a "less than or equal" constraint with this expression as left-hand side.
        Parameters:
        rhs - Right-hand side of new constraint.
        Returns:
        The new constraint.
        Since:
        43.00

      • geq

        public abstract Inequality.Definition geq​(double rhs)
        Create a "greater than or equal" constraint with this expression as left-hand side.
        Parameters:
        rhs - Right-hand side of new constraint.
        Returns:
        The new constraint.
        Since:
        43.00

      • geq

        public abstract Inequality.Definition geq​(Expression rhs)
        Create a "greater than or equal" constraint with this expression as left-hand side.
        Parameters:
        rhs - Right-hand side of new constraint.
        Returns:
        The new constraint.
        Since:
        43.00

      • eq

        public abstract Inequality.Definition eq​(double rhs)
        Create an "equals" constraint with this expression as left-hand side.
        Parameters:
        rhs - Right-hand side of new constraint.
        Returns:
        The new constraint.
        Since:
        43.00

      • eq

        public abstract Inequality.Definition eq​(Expression rhs)
        Create an "equals" constraint with this expression as left-hand side.
        Parameters:
        rhs - Right-hand side of new constraint.
        Returns:
        The new constraint.
        Since:
        43.00

      • in

        public abstract Inequality.Definition in​(double lb,
                                         double ub)
        Create a range constraint that bounds this expression from below and above.
        Parameters:
        lb - Lower bound for this expression.
        ub - Upper bound for this expression.
        Returns:
        The new constraint.
        Since:
        43.00

      • extract

        public abstract boolean extract​(double factor,
                                XPRSprob.RowCreator creator)
        Extract this expression into a row. This is for internal use only, you should never have to call this function explicitly.
        Parameters:
        factor - Factor by which to multiply the expression during extraction.
        creator - The creator to which this expression should be extracted.
        Returns:
        true if the low-level representation does requires normalization (sorting, removal of dups, ...). In some special cases we know that this is not required and can return false to save the overhead.
        Since:
        43.00

      • extract

        public abstract void extract​(double factor,
                             PostfixExtractor extractor)
        Extract this expression into postfix notation.
        Parameters:
        factor - Factor by which to multiply the expression during extraction.
        extractor - The extractor to which the expression is extract.
        Since:
        43.00

      • evaluate

        public abstract double evaluate​(double[] solution)
        Compute the value of this expression with respect to the given solution vector (which is not required to be feasible).
        Parameters:
        solution - Solution values for which the expression is evaluated.
        Since:
        43.00

      • getMaxDegree

        public abstract int getMaxDegree()
        Get the maximum degree of any of the terms/monomials that appear in the symbolic representation of all parenthesized sub-expressions are fully expanded. The maximum degree is
        • 0 for constant expressions.
        • 1 for linear expressions.
        • 2 for quadratic expressions.
        • Integer.MAX_VALUE for function calls or formulas.
        Returns:
        The maximum degree in this function.
        Since:
        43.00

      • getConstantView

        public abstract double getConstantView()
        Get the constant value to which this expression evaluates. If this expression can be treated as a constant value then the function returns the constant value. If the expression cannot be treated as a constant then an exception is raised. In order to test whether the expression can be treated as constant, use function getMaxDegree() and check whether it returns 0.
        Returns:
        The constant represented by this expression.
        Since:
        43.00

      • getLinearView

        public abstract LinearView getLinearView()
        Get a linear read-only view on this expression. If this expression can be treated as a linear expression then the function returns a readonly view on the linear terms (including the constant term if there is any). If the expression cannot be treated as a linear expression then an exception is raised. In order to test this expression can be treated as linear, use function getMaxDegree() and check whether it returns 0 or 1. In the returned java.util.Map.Entry instances the constant term is indicated with a key of XpressProblem.NULL_VARIABLE. Note that depending on the actual expression class and its implementation, the terms may not be presented in the same order in which you added them. There may also be multiple elements with the same key (again depending on the implementation of the actual object).
        Returns:
        View on this linear expression.
        Since:
        43.00

      • getQuadView

        public abstract QuadView getQuadView()
        Get a quadratic read-only view on this expression. If this expression can be treated as a quadratic expression then the function returns a readonly view on the quadratic terms (including the constant term and linear terms if there are any). If the expression cannot be treated as a linear expression then an exception is raised. In order to test this expression can be treated as quadratic, use function getMaxDegree() and check whether it returns 0, 1, or 2. In the returned java.util.Map.Entry instances the constant term is indicated with a key with two XpressProblem.NULL_VARIABLEs. Linear terms are represented by a QPair with XpressProblem.NULL_VARIABLE as second variable. Note that depending on the actual expression class and its implementation, the terms may not be presented in the same order in which you added them. There may also be multiple elements with the same key (again depending on the implementation of the actual object).
        Returns:
        View on this linear expression.
        Since:
        43.00

      • uminus

        public Expression uminus()
        Create a new expression that represents the unary minus of this one.
        Returns:
        Expression representing -this.
        Since:
        43.00

      • plus

        public Expression plus​(Expression arg)
        Create a new expression that represents the sum of this and arg.
        Parameters:
        arg - Addend.
        Returns:
        Sum of this and arg.
        Since:
        43.00

      • plus

        public Expression plus​(double arg)
        Create a new expression that represents the sum of this and arg.
        Parameters:
        arg - Addend.
        Returns:
        Sum of this and arg.
        Since:
        43.00

      • minus

        public Expression minus​(Expression arg)
        Create a new expression that represents the difference of this and arg.
        Parameters:
        arg - Minuend.
        Returns:
        Difference of this and arg.
        Since:
        43.00

      • minus

        public Expression minus​(double arg)
        Create a new expression that represents the difference of this and arg.
        Parameters:
        arg - Minuend.
        Returns:
        Difference of this and arg.
        Since:
        43.00

      • mul

        public Expression mul​(Expression arg)
        Create a new expression that represents the product of this and arg.
        Parameters:
        arg - Factor.
        Returns:
        Product of this and arg.
        Since:
        43.00

      • mul

        public Expression mul​(double arg)
        Create a new expression that represents the product of this and arg.
        Parameters:
        arg - Factor.
        Returns:
        Product of this and arg.
        Since:
        43.00

      • div

        public Expression div​(Expression arg)
        Create a new expression that represents the quotient of this and arg.
        Parameters:
        arg - Divisor.
        Returns:
        Quotient of this and arg.
        Since:
        43.00

      • div

        public Expression div​(double arg)
        Create a new expression that represents the quotient of this and arg.
        Parameters:
        arg - Divisor.
        Returns:
        Quotient of this and arg.
        Since:
        43.00
Parent Topic Class Summary

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