to_univariate_polynomial.h

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#pragma once
 
#include "../MultivariatePolynomial.h"
#include "../UnivariatePolynomial.h"
#include <carl-arith/core/Variables.h>
 
namespace carl {
 
/**
 * Convert a univariate polynomial that is currently (mis)represented by a
 * 'MultivariatePolynomial' into a more appropiate 'UnivariatePolynomial'
 * representation.
 * Note that the current polynomial must mention one and only one variable,
 * i.e., be indeed univariate.
 */
template<typename C, typename O, typename P>
UnivariatePolynomial<C> to_univariate_polynomial(const MultivariatePolynomial<C,O,P>& p) {
    // Only correct when it is already only in one variable.
    assert(variables(p).size() == 1);
    Variable::Arg x = p.lmon()->single_variable();
    std::vector<C> coeffs(p.total_degree()+1,0);
    for (const auto& t : p)
    {
        coeffs[t.tdeg()] = t.coeff();
    }
    return UnivariatePolynomial<C>(x, coeffs);
}
 
/**
 * Convert a multivariate polynomial that is currently represented by a
 * MultivariatePolynomial into a UnivariatePolynomial representation.
 * The main variable of the resulting polynomial is given as second argument.
 */
template<typename C, typename O, typename P>
UnivariatePolynomial<MultivariatePolynomial<C,O,P>> to_univariate_polynomial(const MultivariatePolynomial<C,O,P>& p, Variable v) {
    assert(p.is_consistent());
    std::vector<MultivariatePolynomial<C,O,P>> coeffs(1);
    for (const auto& term: p) {
        if (term.monomial() == nullptr) coeffs[0] += term;
        else {
            const auto& mon = term.monomial();
            auto exponent = mon->exponent_of_variable(v);
            if (exponent >= coeffs.size()) {
                coeffs.resize(exponent + 1);
            }
            std::shared_ptr<const carl::Monomial> tmp = mon->drop_variable(v);
            coeffs[exponent] += term.coeff() * tmp;
        }
    }
    // Convert result back to MultivariatePolynomial and check that the result is equal to p
    assert(MultivariatePolynomial<C>(UnivariatePolynomial<MultivariatePolynomial<C>>(v, coeffs)) == p);
    return UnivariatePolynomial<MultivariatePolynomial<C,O,P>>(v, coeffs);
}
 
}