[PPL-devel] PPL Constraints usage

[Stefan Schupp]

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Hello Roberto,

I created an example which reproduces my problem:

#include <ppl.hh>

int main(int argc, char** argv) {

    using namespace Parma_Polyhedra_Library::IO_Operators;

    Parma_Polyhedra_Library::C_Polyhedron mPolyhedron =
Parma_Polyhedra_Library::C_Polyhedron(2, Parma_Polyhedra_Library::EMPTY);
    Parma_Polyhedra_Library::Variable a(0);
    Parma_Polyhedra_Library::Variable b(1);

    Parma_Polyhedra_Library::Linear_Expression polynom;
    polynom.set_coefficient(a, 1);
    polynom.set_coefficient(b, 3);
    polynom.set_inhomogeneous_term(-4);

    std::cout << "Polynom: " << polynom << std::endl;

    Parma_Polyhedra_Library::Constraint constraint;
    constraint = polynom <= 0;

    std::cout << "Constraint: ";
    constraint.print();
    std::cout << " Dimension: " << constraint.space_dimension()  <<
std::endl;

    mPolyhedron.add_constraint(constraint);

    std::cout << "Polyhedron: ";
    mPolyhedron.print();
    std::cout << std::endl;
}

Am 12/06/14 12:05, schrieb Roberto Bagnara:
> On 11/06/2014 16:29, Stefan Schupp wrote:
>> I am currently trying to create a Polytope from a matrix and a 
>> vector. Therefore I create linear expressions from the
>> coefficients of the matrix in combination with the associated
>> PPL-Variables. Afterwards I can add an inhomogenous term from the
>> given vector.
>> 
>> As far as I read the documentation I can construct a Polytope 
>> naturally by adding constraints. These constraints are supposed
>> to be constructed from a relation of either a linear expression
>> and a constant (my inhomogenuous term, if you want to put it that
>> way) or a relation from two linear expressions. I tried both
>> ways, but the constraint created seems to be empty. How am I
>> supposed to create and use the needed Constraints?
>> 
>> Short example:
>> 
>> Linear expression: A + 3*B - 5 (when printed) resulting
>> constraint: 0 >= -5 (created by:
>> 
>> Parma_Polyhedra_Library::Constraint constraint = expr <= 0
>> 
>> , where expr is the linear expression)
> 
> Hello Stefan,
> 
> please send a piece of code that we can examine, compile and 
> execute. Kind regards,
> 
> Roberto
> 

The created output is:
Polynom: A + 3*B - 4
Constraint: 0 >= -4 Dimension: 0
Polyhedron: false

I thought the constraint created should be something like A + 3*B - 4
<= 0.

Best regards,
Stefan

- -- 
Stefan Schupp M.Sc.
RWTH Aachen University
Computer Science Department, Informatik 2
D-52056 Aachen, Germany
http://www-i2.informatik.rwth-aachen.de/i2/schupp/
Tel.: +49 241 80 21243
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