Nonlinear expressions

[hfossli]

It seems like nonlinear expressions is handled automagically. I don't know if this is by design since the java version throws a "nonlinear expression exception".

// This is a nonlinear expression and should not be supported
BOOST_AUTO_TEST_CASE(variable_is_denominator)
{
    variable x(0), y(0);
    simplex_solver solver;

    BOOST_CHECK_EQUAL(x.value(), 0);
    BOOST_CHECK_EQUAL(y.value(), 0);

    solver.add_constraint(y == 10);

    BOOST_CHECK_EQUAL(x.value(), 0);
    BOOST_CHECK_EQUAL(y.value(), 10);

    solver.add_constraint(x == 5 / y);

    BOOST_CHECK_EQUAL(x.value(), 0.5);
    BOOST_CHECK_EQUAL(y.value(), 10);
}

// This is a linear expression and should be supported
BOOST_AUTO_TEST_CASE(variable_is_numerator)
{
    variable x(0), y(0);
    simplex_solver solver;

    BOOST_CHECK_EQUAL(x.value(), 0);
    BOOST_CHECK_EQUAL(y.value(), 0);

    solver.add_constraint(y == 10);

    BOOST_CHECK_EQUAL(x.value(), 0);
    BOOST_CHECK_EQUAL(y.value(), 10);

    solver.add_constraint(x == y / 5);

    BOOST_CHECK_EQUAL(x.value(), 2);
    BOOST_CHECK_EQUAL(y.value(), 10);
}

Result

Running 41 test cases...
/unit_tests.cpp:777: error in "variable_is_denominator": check x.value() == 0.5 failed [2 != 0.5]

*** 1 failure detected in test suite "rhea"

This is the Rhea implementation

linear_expression& linear_expression::operator/=(const linear_expression& x)
{
    if (is_constant())
        return *this = x / constant();

    if (!x.is_constant())
        throw nonlinear_expression();

    return operator/=(x.constant());
}

This is the java implementation

public final Expression divide(double x)
           throws NonlinearExpression
   {
       if (Util.approx(x, 0.0))
       {
           throw new NonlinearExpression();
       }
       return times(1.0 / x);
   }

[Nocte-]

Nope, that's definitely not supposed to happen. Good catch.

[hfossli]

👍